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Oracle® Database VLDB and Partitioning Guide
11g Release 1 (11.1)

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3 Partition Administration

Partition administration is one of the most important tasks when working with partitioned tables and indexes. This chapter describes various aspects of creating and maintaining partitioned tables and indexes, and contains the following topics:

Note:

Before you attempt to create a partitioned table or index, or perform maintenance operations on any partitioned table, it is recommended that you review the information in Chapter 2, "Partitioning Concepts".

Creating Partitions

Creating a partitioned table or index is very similar to creating a non-partitioned table or index (as described in Oracle Database Administrator's Guide), but you include a partitioning clause in the CREATE TABLE statement. The partitioning clause, and subclauses, that you include depend upon the type of partitioning you want to achieve.

Partitioning is possible on both regular (heap organized) tables and index-organized tables, except for those containing LONG or LONG RAW columns. You can create non-partitioned global indexes, range or hash-partitioned global indexes, and local indexes on partitioned tables.

When you create (or alter) a partitioned table, a row movement clause (either ENABLE ROW MOVEMENT or DISABLE ROW MOVEMENT) can be specified. This clause either enables or disables the migration of a row to a new partition if its key is updated. The default is DISABLE ROW MOVEMENT.

The following sections present details and examples of creating partitions for the various types of partitioned tables and indexes:

See Also:

Creating Range-Partitioned Tables and Global Indexes

The PARTITION BY RANGE clause of the CREATE TABLE statement specifies that the table or index is to be range-partitioned. The PARTITION clauses identify the individual partition ranges, and the optional subclauses of a PARTITION clause can specify physical and other attributes specific to a partition segment. If not overridden at the partition level, partitions inherit the attributes of their underlying table.

Creating a Range Partitioned Table

The following example creates a table of four partitions, one for each quarter of sales. The columns sale_year, sale_month, and sale_day are the partitioning columns, while their values constitute the partitioning key of a specific row. The VALUES LESS THAN clause determines the partition bound: rows with partitioning key values that compare less than the ordered list of values specified by the clause are stored in the partition. Each partition is given a name (sales_q1, sales_q2, ...), and each partition is contained in a separate tablespace (tsa, tsb, ...).

CREATE TABLE sales

  ( prod_id       NUMBER(6)

  , cust_id       NUMBER

  , time_id       DATE

  , channel_id    CHAR(1)

  , promo_id      NUMBER(6)

  , quantity_sold NUMBER(3)

  , amount_sold   NUMBER(10,2)

  )

 PARTITION BY RANGE (time_id)

 ( PARTITION sales_q1_2006 VALUES LESS THAN (TO_DATE('01-APR-2006','dd-MON-yyyy'))

    TABLESPACE tsa

 , PARTITION sales_q2_2006 VALUES LESS THAN (TO_DATE('01-JUL-2006','dd-MON-yyyy'))

    TABLESPACE tsb

 , PARTITION sales_q3_2006 VALUES LESS THAN (TO_DATE('01-OCT-2006','dd-MON-yyyy'))

    TABLESPACE tsc

 , PARTITION sales_q4_2006 VALUES LESS THAN (TO_DATE('01-JAN-2007','dd-MON-yyyy'))

    TABLESPACE tsd

 );

A row with time_id=17-MAR-2006 would be stored in partition sales_q1_2006.

In the following example, more complexity is added to the example presented earlier for a range-partitioned table. Storage parameters and a LOGGING attribute are specified at the table level. These replace the corresponding defaults inherited from the tablespace level for the table itself, and are inherited by the range partitions. However, because there was little business in the first quarter, the storage attributes for partition sales_q1_2006 are made smaller. The ENABLE ROW MOVEMENT clause is specified to allow the automatic migration of a row to a new partition if an update to a key value is made that would place the row in a different partition.

CREATE TABLE sales

  ( prod_id       NUMBER(6)

  , cust_id       NUMBER

  , time_id       DATE

  , channel_id    CHAR(1)

  , promo_id      NUMBER(6)

  , quantity_sold NUMBER(3)

  , amount_sold   NUMBER(10,2)

  )

 STORAGE (INITIAL 100K NEXT 50K) LOGGING

 PARTITION BY RANGE (time_id)

 ( PARTITION sales_q1_2006 VALUES LESS THAN (TO_DATE('01-APR-2006','dd-MON-yyyy'))

    TABLESPACE tsa STORAGE (INITIAL 20K NEXT 10K)

 , PARTITION sales_q2_2006 VALUES LESS THAN (TO_DATE('01-JUL-2006','dd-MON-yyyy'))

    TABLESPACE tsb

 , PARTITION sales_q3_2006 VALUES LESS THAN (TO_DATE('01-OCT-2006','dd-MON-yyyy'))

    TABLESPACE tsc

 , PARTITION sales_q4_2006 VALUES LESS THAN (TO_DATE('01-JAN-2007','dd-MON-yyyy'))

    TABLESPACE tsd

 )

 ENABLE ROW MOVEMENT;

Creating a Range-Partitioned Global Index

The rules for creating range-partitioned global indexes are similar to those for creating range-partitioned tables. The following is an example of creating a range-partitioned global index on sale_month for the tables created in the preceding examples. Each index partition is named but is stored in the default tablespace for the index.

CREATE INDEX amount_sold_ix ON sales(amount_sold)

   GLOBAL PARTITION BY RANGE(sale_month)

      ( PARTITION p_100 VALUES LESS THAN (100)

      , PARTITION p_1000 VALUES LESS THAN (1000)

      , PARTITION p_10000 VALUES LESS THAN (10000)

      , PARTITION p_100000 VALUES LESS THAN (100000)

      , PARTITION p_1000000 VALUES LESS THAN (1000000)

      , PARTITION p_greater_than_1000000 VALUES LESS THAN (maxvalue)

      );

Note:

If your enterprise has or will have databases using different character sets, use caution when partitioning on character columns, because the sort sequence of characters is not identical in all character sets. For more information, see Oracle Database Globalization Support Guide.

Creating Interval-Partitioned Tables

The INTERVAL clause of the CREATE TABLE statement establishes interval partitioning for the table. You must specify at least one range partition using the PARTITION clause. The range partitioning key value determines the high value of the range partitions, which is called the transition point, and the database automatically creates interval partitions for data beyond that transition point. The lower boundary of every interval partition is the non-inclusive upper boundary of the previous range or interval partition.

For example, if you create an interval partitioned table with monthly intervals and the transition point at January 1, 2007, then the lower boundary for the January 2007 interval is January 1, 2007. The lower boundary for the July 2007 interval is July 1, 2007, regardless of whether the June 2007 partition was already created.

For interval partitioning, the partitioning key can only be a single column name from the table and it must be of NUMBER or DATE type. The optional STORE IN clause lets you specify one or more tablespaces into which the database will store interval partition data using a round-robin algorithm for subsequently created interval partitions.

The following example specifies four partitions with varying widths. It also specifies that above the transition point of January 1, 2007, partitions are created with a width of one month.

CREATE TABLE interval_sales

    ( prod_id        NUMBER(6)

    , cust_id        NUMBER

    , time_id        DATE

    , channel_id     CHAR(1)

    , promo_id       NUMBER(6)

    , quantity_sold  NUMBER(3)

    , amount_sold    NUMBER(10,2)

    ) 

  PARTITION BY RANGE (time_id) 

  INTERVAL(NUMTOYMINTERVAL(1, 'MONTH'))

    ( PARTITION p0 VALUES LESS THAN (TO_DATE('1-1-2005', 'DD-MM-YYYY')),

      PARTITION p1 VALUES LESS THAN (TO_DATE('1-1-2006', 'DD-MM-YYYY')),

      PARTITION p2 VALUES LESS THAN (TO_DATE('1-7-2006', 'DD-MM-YYYY')),

      PARTITION p3 VALUES LESS THAN (TO_DATE('1-1-2007', 'DD-MM-YYYY')) );

The high bound of partition p3 represents the transition point. p3 and all partitions below it (p0, p1, and p2 in this example) are in the range section while all partitions above it fall into the interval section.

Creating Hash-Partitioned Tables and Global Indexes

The PARTITION BY HASH clause of the CREATE TABLE statement identifies that the table is to be hash-partitioned. The PARTITIONS clause can then be used to specify the number of partitions to create, and optionally, the tablespaces to store them in. Alternatively, you can use PARTITION clauses to name the individual partitions and their tablespaces.

The only attribute you can specify for hash partitions is TABLESPACE. All of the hash partitions of a table must share the same segment attributes (except TABLESPACE), which are inherited from the table level.

Creating a Hash Partitioned Table

The following example creates a hash-partitioned table. The partitioning column is id, four partitions are created and assigned system generated names, and they are placed in four named tablespaces (gear1, gear2, ...).

CREATE TABLE scubagear

     (id NUMBER,

      name VARCHAR2 (60))

   PARTITION BY HASH (id)

   PARTITIONS 4 

   STORE IN (gear1, gear2, gear3, gear4);

The following examples illustrate two methods of creating a hash-partitioned table named dept. In the first example the number of partitions is specified, but system generated names are assigned to them and they are stored in the default tablespace of the table.

CREATE TABLE dept (deptno NUMBER, deptname VARCHAR(32))

     PARTITION BY HASH(deptno) PARTITIONS 16;

In the following example, names of individual partitions, and tablespaces in which they are to reside, are specified. The initial extent size for each hash partition (segment) is also explicitly stated at the table level, and all partitions inherit this attribute.

CREATE TABLE dept (deptno NUMBER, deptname VARCHAR(32))

     STORAGE (INITIAL 10K)

     PARTITION BY HASH(deptno)

       (PARTITION p1 TABLESPACE ts1, PARTITION p2 TABLESPACE ts2,

        PARTITION p3 TABLESPACE ts1, PARTITION p4 TABLESPACE ts3);

If you create a local index for this table, the database constructs the index so that it is equipartitioned with the underlying table. The database also ensures that the index is maintained automatically when maintenance operations are performed on the underlying table. The following is an example of creating a local index on the table dept:

CREATE INDEX loc_dept_ix ON dept(deptno) LOCAL;

You can optionally name the hash partitions and tablespaces into which the local index partitions are to be stored, but if you do not do so, the database uses the name of the corresponding base partition as the index partition name, and stores the index partition in the same tablespace as the table partition.

Creating a Hash-Partitioned Global Index

Hash-partitioned global indexes can improve the performance of indexes where a small number of leaf blocks in the index have high contention in multiuser OLTP environments. Hash-partitioned global indexes can also limit the impact of index skew on monotonously increasing column values. Queries involving the equality and IN predicates on the index partitioning key can efficiently use hash-partitioned global indexes.

The syntax for creating a hash partitioned global index is similar to that used for a hash partitioned table. For example, the following statement creates a hash-partitioned global index:

CREATE INDEX hgidx ON tab (c1,c2,c3) GLOBAL

     PARTITION BY HASH (c1,c2)

     (PARTITION p1  TABLESPACE tbs_1,

      PARTITION p2  TABLESPACE tbs_2,

      PARTITION p3  TABLESPACE tbs_3,

      PARTITION p4  TABLESPACE tbs_4);

Creating List-Partitioned Tables

The semantics for creating list partitions are very similar to those for creating range partitions. However, to create list partitions, you specify a PARTITION BY LIST clause in the CREATE TABLE statement, and the PARTITION clauses specify lists of literal values, which are the discrete values of the partitioning columns that qualify rows to be included in the partition. For list partitioning, the partitioning key can only be a single column name from the table.

Available only with list partitioning, you can use the keyword DEFAULT to describe the value list for a partition. This identifies a partition that will accommodate rows that do not map into any of the other partitions.

As with range partitions, optional subclauses of a PARTITION clause can specify physical and other attributes specific to a partition segment. If not overridden at the partition level, partitions inherit the attributes of their parent table.

The following example creates a list-partitioned table. It creates table q1_sales_by_region which is partitioned by regions consisting of groups of U.S. states.

CREATE TABLE q1_sales_by_region

      (deptno number, 

       deptname varchar2(20),

       quarterly_sales number(10, 2),

       state varchar2(2))

   PARTITION BY LIST (state)

      (PARTITION q1_northwest VALUES ('OR', 'WA'),

       PARTITION q1_southwest VALUES ('AZ', 'UT', 'NM'),

       PARTITION q1_northeast VALUES  ('NY', 'VM', 'NJ'),

       PARTITION q1_southeast VALUES ('FL', 'GA'),

       PARTITION q1_northcentral VALUES ('SD', 'WI'),

       PARTITION q1_southcentral VALUES ('OK', 'TX'));

A row is mapped to a partition by checking whether the value of the partitioning column for a row matches a value in the value list that describes the partition.

For example, some sample rows are inserted as follows:

  • (10, 'accounting', 100, 'WA') maps to partition q1_northwest

  • (20, 'R&D', 150, 'OR') maps to partition q1_northwest

  • (30, 'sales', 100, 'FL') maps to partition q1_southeast

  • (40, 'HR', 10, 'TX') maps to partition q1_southwest

  • (50, 'systems engineering', 10, 'CA') does not map to any partition in the table and raises an error

Unlike range partitioning, with list partitioning, there is no apparent sense of order between partitions. You can also specify a default partition into which rows that do not map to any other partition are mapped. If a default partition were specified in the preceding example, the state CA would map to that partition.

The following example creates table sales_by_region and partitions it using the list method. The first two PARTITION clauses specify physical attributes, which override the table-level defaults. The remaining PARTITION clauses do not specify attributes and those partitions inherit their physical attributes from table-level defaults. A default partition is also specified.

CREATE TABLE sales_by_region (item# INTEGER, qty INTEGER, 

             store_name VARCHAR(30), state_code VARCHAR(2),

             sale_date DATE)

     STORAGE(INITIAL 10K NEXT 20K) TABLESPACE tbs5 

     PARTITION BY LIST (state_code) 

     (

     PARTITION region_east

        VALUES ('MA','NY','CT','NH','ME','MD','VA','PA','NJ')

        STORAGE (INITIAL 20K NEXT 40K PCTINCREASE 50) 

        TABLESPACE tbs8,

     PARTITION region_west

        VALUES ('CA','AZ','NM','OR','WA','UT','NV','CO')

        NOLOGGING,

     PARTITION region_south

        VALUES ('TX','KY','TN','LA','MS','AR','AL','GA'),

     PARTITION region_central 

        VALUES ('OH','ND','SD','MO','IL','MI','IA'),

     PARTITION region_null

        VALUES (NULL),

     PARTITION region_unknown

        VALUES (DEFAULT)

     );

Creating Reference-Partitioned Tables

To create a reference-partitioned table, you specify a PARTITION BY REFERENCE clause in the CREATE TABLE statement. This clause specifies the name of a referential constraint and this constraint becomes the partitioning referential constraint that is used as the basis for reference partitioning in the table. The referential constraint must be enabled and enforced.

As with other partitioned tables, you can specify object-level default attributes, and you can optionally specify partition descriptors that override the object-level defaults on a per-partition basis.

The following example creates a parent table orders which is range-partitioned on order_date. The reference-partitioned child table order_items is created with four partitions, Q1_2005, Q2_2005, Q3_2005, and Q4_2005, where each partition contains the order_items rows corresponding to orders in the respective parent partition.

CREATE TABLE orders

    ( order_id           NUMBER(12),

      order_date         TIMESTAMP WITH LOCAL TIME ZONE,

      order_mode         VARCHAR2(8),

      customer_id        NUMBER(6),

      order_status       NUMBER(2),

      order_total        NUMBER(8,2),

      sales_rep_id       NUMBER(6),

      promotion_id       NUMBER(6),

      CONSTRAINT orders_pk PRIMARY KEY(order_id)

    )

  PARTITION BY RANGE(order_date)

    ( PARTITION Q1_2005 VALUES LESS THAN (TO_DATE('01-APR-2005','DD-MON-YYYY')),

      PARTITION Q2_2005 VALUES LESS THAN (TO_DATE('01-JUL-2005','DD-MON-YYYY')),

      PARTITION Q3_2005 VALUES LESS THAN (TO_DATE('01-OCT-2005','DD-MON-YYYY')),

      PARTITION Q4_2005 VALUES LESS THAN (TO_DATE('01-JAN-2006','DD-MON-YYYY'))

    );


CREATE TABLE order_items

    ( order_id           NUMBER(12) NOT NULL,

      line_item_id       NUMBER(3)  NOT NULL,

      product_id         NUMBER(6)  NOT NULL,

      unit_price         NUMBER(8,2),

      quantity           NUMBER(8),

      CONSTRAINT order_items_fk

      FOREIGN KEY(order_id) REFERENCES orders(order_id)

    )

    PARTITION BY REFERENCE(order_items_fk);

If partition descriptors are provided, then the number of partitions described must exactly equal the number of partitions or subpartitions in the referenced table. If the parent table is a composite partitioned table, then the table will have one partition for each subpartition of its parent; otherwise the table will have one partition for each partition of its parent.

Partition bounds cannot be specified for the partitions of a reference-partitioned table.

The partitions of a reference-partitioned table can be named. If a partition is not explicitly named, then it will inherit its name from the corresponding partition in the parent table, unless this inherited name conflicts with one of the explicit names given. In this case, the partition will have a system-generated name.

Partitions of a reference-partitioned table will collocate with the corresponding partition of the parent table, if no explicit tablespace is specified for the reference-partitioned table's partition.

Creating Composite Partitioned Tables

To create a composite partitioned table, you start by using the PARTITION BY [ RANGE | LIST ] clause of a CREATE TABLE statement. Next, you specify a SUBPARTITION BY [ RANGE | LIST | HASH ] clause that follows similar syntax and rules as the PARTITION BY [ RANGE | LIST | HASH ] clause. The individual PARTITION and SUBPARTITION or SUBPARTITIONS clauses, and optionally a SUBPARTITION TEMPLATE clause, follow.

Creating Composite Range-Hash Partitioned Tables

The following statement creates a range-hash partitioned table. In this example, four range partitions are created, each containing eight subpartitions. Because the subpartitions are not named, system generated names are assigned, but the STORE IN clause distributes them across the 4 specified tablespaces (ts1, ...,ts4).

CREATE TABLE sales

  ( prod_id       NUMBER(6)

  , cust_id       NUMBER

  , time_id       DATE

  , channel_id    CHAR(1)

  , promo_id      NUMBER(6)

  , quantity_sold NUMBER(3)

  , amount_sold   NUMBER(10,2)

  )

 PARTITION BY RANGE (time_id) SUBPARTITION BY HASH (cust_id)

  SUBPARTITIONS 8 STORE IN (ts1, ts2, ts3, ts4)

 ( PARTITION sales_q1_2006 VALUES LESS THAN (TO_DATE('01-APR-2006','dd-MON-yyyy'))

 , PARTITION sales_q2_2006 VALUES LESS THAN (TO_DATE('01-JUL-2006','dd-MON-yyyy'))

 , PARTITION sales_q3_2006 VALUES LESS THAN (TO_DATE('01-OCT-2006','dd-MON-yyyy'))

 , PARTITION sales_q4_2006 VALUES LESS THAN (TO_DATE('01-JAN-2007','dd-MON-yyyy'))

 );

The partitions of a range-hash partitioned table are logical structures only, as their data is stored in the segments of their subpartitions. As with partitions, these subpartitions share the same logical attributes. Unlike range partitions in a range-partitioned table, the subpartitions cannot have different physical attributes from the owning partition, although they are not required to reside in the same tablespace.

Attributes specified for a range partition apply to all subpartitions of that partition. You can specify different attributes for each range partition, and you can specify a STORE IN clause at the partition level if the list of tablespaces across which the subpartitions of that partition should be spread is different from those of other partitions. All of this is illustrated in the following example.

CREATE TABLE emp (deptno NUMBER, empname VARCHAR(32), grade NUMBER)   

     PARTITION BY RANGE(deptno) SUBPARTITION BY HASH(empname)

        SUBPARTITIONS 8 STORE IN (ts1, ts3, ts5, ts7)

    (PARTITION p1 VALUES LESS THAN (1000),

     PARTITION p2 VALUES LESS THAN (2000)

        STORE IN (ts2, ts4, ts6, ts8),

     PARTITION p3 VALUES LESS THAN (MAXVALUE)

       (SUBPARTITION p3_s1 TABLESPACE ts4,

        SUBPARTITION p3_s2 TABLESPACE ts5));

To learn how using a subpartition template can simplify the specification of a composite partitioned table, see "Using Subpartition Templates to Describe Composite Partitioned Tables".

The following statement is an example of creating a local index on the emp table where the index segments are spread across tablespaces ts7, ts8, and ts9.

CREATE INDEX emp_ix ON emp(deptno)

     LOCAL STORE IN (ts7, ts8, ts9);

This local index is equipartitioned with the base table as follows:

  • It consists of as many partitions as the base table.

  • Each index partition consists of as many subpartitions as the corresponding base table partition.

  • Index entries for rows in a given subpartition of the base table are stored in the corresponding subpartition of the index.

Creating Composite Range-List Partitioned Tables

The range partitions of a range-list composite partitioned table are described as for non-composite range partitioned tables. This allows that optional subclauses of a PARTITION clause can specify physical and other attributes, including tablespace, specific to a partition segment. If not overridden at the partition level, partitions inherit the attributes of their underlying table.

The list subpartition descriptions, in the SUBPARTITION clauses, are described as for non-composite list partitions, except the only physical attribute that can be specified is a tablespace (optional). Subpartitions inherit all other physical attributes from the partition description.

The following example illustrates how range-list partitioning might be used. The example tracks sales data of products by quarters and within each quarter, groups it by specified states.

CREATE TABLE quarterly_regional_sales

      (deptno number, item_no varchar2(20),

       txn_date date, txn_amount number, state varchar2(2))

  TABLESPACE ts4

  PARTITION BY RANGE (txn_date)

    SUBPARTITION BY LIST (state)

      (PARTITION q1_1999 VALUES LESS THAN (TO_DATE('1-APR-1999','DD-MON-YYYY'))

         (SUBPARTITION q1_1999_northwest VALUES ('OR', 'WA'),

          SUBPARTITION q1_1999_southwest VALUES ('AZ', 'UT', 'NM'),

          SUBPARTITION q1_1999_northeast VALUES ('NY', 'VM', 'NJ'),

          SUBPARTITION q1_1999_southeast VALUES ('FL', 'GA'),

          SUBPARTITION q1_1999_northcentral VALUES ('SD', 'WI'),

          SUBPARTITION q1_1999_southcentral VALUES ('OK', 'TX')

         ),

       PARTITION q2_1999 VALUES LESS THAN ( TO_DATE('1-JUL-1999','DD-MON-YYYY'))

         (SUBPARTITION q2_1999_northwest VALUES ('OR', 'WA'),

          SUBPARTITION q2_1999_southwest VALUES ('AZ', 'UT', 'NM'),

          SUBPARTITION q2_1999_northeast VALUES ('NY', 'VM', 'NJ'),

          SUBPARTITION q2_1999_southeast VALUES ('FL', 'GA'),

          SUBPARTITION q2_1999_northcentral VALUES ('SD', 'WI'),

          SUBPARTITION q2_1999_southcentral VALUES ('OK', 'TX')

         ),

       PARTITION q3_1999 VALUES LESS THAN (TO_DATE('1-OCT-1999','DD-MON-YYYY'))

         (SUBPARTITION q3_1999_northwest VALUES ('OR', 'WA'),

          SUBPARTITION q3_1999_southwest VALUES ('AZ', 'UT', 'NM'),

          SUBPARTITION q3_1999_northeast VALUES ('NY', 'VM', 'NJ'),

          SUBPARTITION q3_1999_southeast VALUES ('FL', 'GA'),

          SUBPARTITION q3_1999_northcentral VALUES ('SD', 'WI'),

          SUBPARTITION q3_1999_southcentral VALUES ('OK', 'TX')

         ),

       PARTITION q4_1999 VALUES LESS THAN ( TO_DATE('1-JAN-2000','DD-MON-YYYY'))

         (SUBPARTITION q4_1999_northwest VALUES ('OR', 'WA'),

          SUBPARTITION q4_1999_southwest VALUES ('AZ', 'UT', 'NM'),

          SUBPARTITION q4_1999_northeast VALUES ('NY', 'VM', 'NJ'),

          SUBPARTITION q4_1999_southeast VALUES ('FL', 'GA'),

          SUBPARTITION q4_1999_northcentral VALUES ('SD', 'WI'),

          SUBPARTITION q4_1999_southcentral VALUES ('OK', 'TX')

         )

      );

A row is mapped to a partition by checking whether the value of the partitioning column for a row falls within a specific partition range. The row is then mapped to a subpartition within that partition by identifying the subpartition whose descriptor value list contains a value matching the subpartition column value.

For example, some sample rows are inserted as follows:

  • (10, 4532130, '23-Jan-1999', 8934.10, 'WA') maps to subpartition q1_1999_northwest

  • (20, 5671621, '15-May-1999', 49021.21, 'OR') maps to subpartition q2_1999_northwest

  • (30, 9977612, '07-Sep-1999', 30987.90, 'FL') maps to subpartition q3_1999_southeast

  • (40, 9977612, '29-Nov-1999', 67891.45, 'TX') maps to subpartition q4_1999_southcentral

  • (40, 4532130, '5-Jan-2000', 897231.55, 'TX') does not map to any partition in the table and raises an error

  • (50, 5671621, '17-Dec-1999', 76123.35, 'CA') does not map to any subpartition in the table and raises an error

The partitions of a range-list partitioned table are logical structures only, as their data is stored in the segments of their subpartitions. The list subpartitions have the same characteristics as list partitions. You can specify a default subpartition, just as you specify a default partition for list partitioning.

The following example creates a table that specifies a tablespace at the partition and subpartition levels. The number of subpartitions within each partition varies, and default subpartitions are specified.

CREATE TABLE sample_regional_sales

      (deptno number, item_no varchar2(20),

       txn_date date, txn_amount number, state varchar2(2))

  PARTITION BY RANGE (txn_date)

    SUBPARTITION BY LIST (state)

      (PARTITION q1_1999 VALUES LESS THAN (TO_DATE('1-APR-1999','DD-MON-YYYY'))

          TABLESPACE tbs_1

         (SUBPARTITION q1_1999_northwest VALUES ('OR', 'WA'),

          SUBPARTITION q1_1999_southwest VALUES ('AZ', 'UT', 'NM'),

          SUBPARTITION q1_1999_northeast VALUES ('NY', 'VM', 'NJ'),

          SUBPARTITION q1_1999_southeast VALUES ('FL', 'GA'),

          SUBPARTITION q1_others VALUES (DEFAULT) TABLESPACE tbs_4

         ),

       PARTITION q2_1999 VALUES LESS THAN ( TO_DATE('1-JUL-1999','DD-MON-YYYY'))

          TABLESPACE tbs_2

         (SUBPARTITION q2_1999_northwest VALUES ('OR', 'WA'),

          SUBPARTITION q2_1999_southwest VALUES ('AZ', 'UT', 'NM'),

          SUBPARTITION q2_1999_northeast VALUES ('NY', 'VM', 'NJ'),

          SUBPARTITION q2_1999_southeast VALUES ('FL', 'GA'),

          SUBPARTITION q2_1999_northcentral VALUES ('SD', 'WI'),

          SUBPARTITION q2_1999_southcentral VALUES ('OK', 'TX')

         ),

       PARTITION q3_1999 VALUES LESS THAN (TO_DATE('1-OCT-1999','DD-MON-YYYY'))

          TABLESPACE tbs_3

         (SUBPARTITION q3_1999_northwest VALUES ('OR', 'WA'),

          SUBPARTITION q3_1999_southwest VALUES ('AZ', 'UT', 'NM'),

          SUBPARTITION q3_others VALUES (DEFAULT) TABLESPACE tbs_4

         ),

       PARTITION q4_1999 VALUES LESS THAN ( TO_DATE('1-JAN-2000','DD-MON-YYYY'))

          TABLESPACE tbs_4

      );

This example results in the following subpartition descriptions:

  • All subpartitions inherit their physical attributes, other than tablespace, from tablespace level defaults. This is because the only physical attribute that has been specified for partitions or subpartitions is tablespace. There are no table level physical attributes specified, thus tablespace level defaults are inherited at all levels.

  • The first 4 subpartitions of partition q1_1999 are all contained in tbs_1, except for the subpartition q1_others, which is stored in tbs_4 and contains all rows that do not map to any of the other partitions.

  • The 6 subpartitions of partition q2_1999 are all stored in tbs_2.

  • The first 2 subpartitions of partition q3_1999 are all contained in tbs_3, except for the subpartition q3_others, which is stored in tbs_4 and contains all rows that do not map to any of the other partitions.

  • There is no subpartition description for partition q4_1999. This results in one default subpartition being created and stored in tbs_4. The subpartition name is system generated in the form SYS_SUBPn.

To learn how using a subpartition template can simplify the specification of a composite partitioned table, see "Using Subpartition Templates to Describe Composite Partitioned Tables".

Creating Composite Range-Range Partitioned Tables

The range partitions of a range-range composite partitioned table are described as for non-composite range partitioned tables. This allows that optional subclauses of a PARTITION clause can specify physical and other attributes, including tablespace, specific to a partition segment. If not overridden at the partition level, partitions inherit the attributes of their underlying table.

The range subpartition descriptions, in the SUBPARTITION clauses, are described as for non-composite range partitions, except the only physical attribute that can be specified is an optional tablespace. Subpartitions inherit all other physical attributes from the partition description.

The following example illustrates how range-range partitioning might be used. The example tracks shipments. The service level agreement with the customer states that every order will be delivered in the calendar month after the order was placed. The following types of orders are identified:

  • E (EARLY): orders that are delivered before the the middle of the next month after the order was placed. These orders likely exceed customers' expectations.

  • A (AGREED): orders that are delivered in the calendar month after the order was placed (but not early orders).

  • L (LATE): orders that were only delivered starting the second calendar month after the order was placed.

CREATE TABLE shipments

( order_id      NUMBER NOT NULL

, order_date    DATE NOT NULL

, delivery_date DATE NOT NULL

, customer_id   NUMBER NOT NULL

, sales_amount  NUMBER NOT NULL

)

PARTITION BY RANGE (order_date)

SUBPARTITION BY RANGE (delivery_date)

( PARTITION p_2006_jul VALUES LESS THAN (TO_DATE('01-AUG-2006','dd-MON-yyyy'))

  ( SUBPARTITION p06_jul_e VALUES LESS THAN (TO_DATE('15-AUG-2006','dd-MON-yyyy'))

  , SUBPARTITION p06_jul_a VALUES LESS THAN (TO_DATE('01-SEP-2006','dd-MON-yyyy'))

  , SUBPARTITION p06_jul_l VALUES LESS THAN (MAXVALUE)

  )

, PARTITION p_2006_aug VALUES LESS THAN (TO_DATE('01-SEP-2006','dd-MON-yyyy'))

  ( SUBPARTITION p06_aug_e VALUES LESS THAN (TO_DATE('15-SEP-2006','dd-MON-yyyy'))

  , SUBPARTITION p06_aug_a VALUES LESS THAN (TO_DATE('01-OCT-2006','dd-MON-yyyy'))

  , SUBPARTITION p06_aug_l VALUES LESS THAN (MAXVALUE)

  )

, PARTITION p_2006_sep VALUES LESS THAN (TO_DATE('01-OCT-2006','dd-MON-yyyy'))

  ( SUBPARTITION p06_sep_e VALUES LESS THAN (TO_DATE('15-OCT-2006','dd-MON-yyyy'))

  , SUBPARTITION p06_sep_a VALUES LESS THAN (TO_DATE('01-NOV-2006','dd-MON-yyyy'))

  , SUBPARTITION p06_sep_l VALUES LESS THAN (MAXVALUE)

  )

, PARTITION p_2006_oct VALUES LESS THAN (TO_DATE('01-NOV-2006','dd-MON-yyyy'))

  ( SUBPARTITION p06_oct_e VALUES LESS THAN (TO_DATE('15-NOV-2006','dd-MON-yyyy'))

  , SUBPARTITION p06_oct_a VALUES LESS THAN (TO_DATE('01-DEC-2006','dd-MON-yyyy'))

  , SUBPARTITION p06_oct_l VALUES LESS THAN (MAXVALUE)

  )

, PARTITION p_2006_nov VALUES LESS THAN (TO_DATE('01-DEC-2006','dd-MON-yyyy'))

  ( SUBPARTITION p06_nov_e VALUES LESS THAN (TO_DATE('15-DEC-2006','dd-MON-yyyy'))

  , SUBPARTITION p06_nov_a VALUES LESS THAN (TO_DATE('01-JAN-2007','dd-MON-yyyy'))

  , SUBPARTITION p06_nov_l VALUES LESS THAN (MAXVALUE)

  )

, PARTITION p_2006_dec VALUES LESS THAN (TO_DATE('01-JAN-2007','dd-MON-yyyy'))

  ( SUBPARTITION p06_dec_e VALUES LESS THAN (TO_DATE('15-JAN-2007','dd-MON-yyyy'))

  , SUBPARTITION p06_dec_a VALUES LESS THAN (TO_DATE('01-FEB-2007','dd-MON-yyyy'))

  , SUBPARTITION p06_dec_l VALUES LESS THAN (MAXVALUE)

  )

);

A row is mapped to a partition by checking whether the value of the partitioning column for a row falls within a specific partition range. The row is then mapped to a subpartition within that partition by identifying whether the value of the subpartitioning column falls within a specific range. For example, a shipment with an order date in September 2006 and a delivery date of October 28, 2006 falls in partition p06_oct_a.

To learn how using a subpartition template can simplify the specification of a composite partitioned table, see "Using Subpartition Templates to Describe Composite Partitioned Tables".

Creating Composite List-* Partitioned Tables

The concepts of list-hash, list-list, and list-range composite partitioning are similar to the concepts for range-hash, range-list, and range-range partitioning. This time, however, you specify PARTITION BY LIST to define the partitioning strategy.

The list partitions of a list-* composite partitioned table are described as for non-composite range partitioned tables. This allows that optional subclauses of a PARTITION clause can specify physical and other attributes, including tablespace, specific to a partition segment. If not overridden at the partition level, then partitions inherit the attributes of their underlying table.

The subpartition descriptions, in the SUBPARTITION or SUBPARTITIONS clauses, are described as for range-* composite partitioning methods.

See Also:

The following sections show examples for the different list-* composite partitioning methods.

Creating Composite List-Hash Partitioned Tables

The following example shows an accounts table that is list partitioned by region and subpartitioned using hash by customer identifier.

CREATE TABLE accounts

( id             NUMBER

, account_number NUMBER

, customer_id    NUMBER

, balance        NUMBER

, branch_id      NUMBER

, region         VARCHAR(2)

, status         VARCHAR2(1)

)

PARTITION BY LIST (region)

SUBPARTITION BY HASH (customer_id) SUBPARTITIONS 8

( PARTITION p_northwest VALUES ('OR', 'WA')

, PARTITION p_southwest VALUES ('AZ', 'UT', 'NM')

, PARTITION p_northeast VALUES ('NY', 'VM', 'NJ')

, PARTITION p_southeast VALUES ('FL', 'GA')

, PARTITION p_northcentral VALUES ('SD', 'WI')

, PARTITION p_southcentral VALUES ('OK', 'TX')

);

To learn how using a subpartition template can simplify the specification of a composite partitioned table, see "Using Subpartition Templates to Describe Composite Partitioned Tables".

Creating Composite List-List Partitioned Tables

The following example shows an accounts table that is list partitioned by region and subpartitioned using list by account status.

CREATE TABLE accounts

( id             NUMBER

, account_number NUMBER

, customer_id    NUMBER

, balance        NUMBER

, branch_id      NUMBER

, region         VARCHAR(2)

, status         VARCHAR2(1)

)

PARTITION BY LIST (region)

SUBPARTITION BY LIST (status)

( PARTITION p_northwest VALUES ('OR', 'WA')

  ( SUBPARTITION p_nw_bad VALUES ('B')

  , SUBPARTITION p_nw_average VALUES ('A')

  , SUBPARTITION p_nw_good VALUES ('G')

  )

, PARTITION p_southwest VALUES ('AZ', 'UT', 'NM')

  ( SUBPARTITION p_sw_bad VALUES ('B')

  , SUBPARTITION p_sw_average VALUES ('A')

  , SUBPARTITION p_sw_good VALUES ('G')

  )

, PARTITION p_northeast VALUES ('NY', 'VM', 'NJ')

  ( SUBPARTITION p_ne_bad VALUES ('B')

  , SUBPARTITION p_ne_average VALUES ('A')

  , SUBPARTITION p_ne_good VALUES ('G')

  )

, PARTITION p_southeast VALUES ('FL', 'GA')

  ( SUBPARTITION p_se_bad VALUES ('B')

  , SUBPARTITION p_se_average VALUES ('A')

  , SUBPARTITION p_se_good VALUES ('G')

  )

, PARTITION p_northcentral VALUES ('SD', 'WI')

  ( SUBPARTITION p_nc_bad VALUES ('B')

  , SUBPARTITION p_nc_average VALUES ('A')

  , SUBPARTITION p_nc_good VALUES ('G')

  )

, PARTITION p_southcentral VALUES ('OK', 'TX')

  ( SUBPARTITION p_sc_bad VALUES ('B')

  , SUBPARTITION p_sc_average VALUES ('A')

  , SUBPARTITION p_sc_good VALUES ('G')

  )

);

To learn how using a subpartition template can simplify the specification of a composite partitioned table, see "Using Subpartition Templates to Describe Composite Partitioned Tables".

Creating Composite List-Range Partitioned Tables

The following example shows an accounts table that is list partitioned by region and subpartitioned using range by account balance. Note that row movement is enabled. Subpartitions for different list partitions could have different ranges specified.

CREATE TABLE accounts

( id             NUMBER

, account_number NUMBER

, customer_id    NUMBER

, balance        NUMBER

, branch_id      NUMBER

, region         VARCHAR(2)

, status         VARCHAR2(1)

)

PARTITION BY LIST (region)

SUBPARTITION BY RANGE (balance)

( PARTITION p_northwest VALUES ('OR', 'WA')

  ( SUBPARTITION p_nw_low VALUES LESS THAN (1000)

  , SUBPARTITION p_nw_average VALUES LESS THAN (10000)

  , SUBPARTITION p_nw_high VALUES LESS THAN (100000)

  , SUBPARTITION p_nw_extraordinary VALUES LESS THAN (MAXVALUE)

  )

, PARTITION p_southwest VALUES ('AZ', 'UT', 'NM')

  ( SUBPARTITION p_sw_low VALUES LESS THAN (1000)

  , SUBPARTITION p_sw_average VALUES LESS THAN (10000)

  , SUBPARTITION p_sw_high VALUES LESS THAN (100000)

  , SUBPARTITION p_sw_extraordinary VALUES LESS THAN (MAXVALUE)

  )

, PARTITION p_northeast VALUES ('NY', 'VM', 'NJ')

  ( SUBPARTITION p_ne_low VALUES LESS THAN (1000)

  , SUBPARTITION p_ne_average VALUES LESS THAN (10000)

  , SUBPARTITION p_ne_high VALUES LESS THAN (100000)

  , SUBPARTITION p_ne_extraordinary VALUES LESS THAN (MAXVALUE)

  )

, PARTITION p_southeast VALUES ('FL', 'GA')

  ( SUBPARTITION p_se_low VALUES LESS THAN (1000)

  , SUBPARTITION p_se_average VALUES LESS THAN (10000)

  , SUBPARTITION p_se_high VALUES LESS THAN (100000)

  , SUBPARTITION p_se_extraordinary VALUES LESS THAN (MAXVALUE)

  )

, PARTITION p_northcentral VALUES ('SD', 'WI')

  ( SUBPARTITION p_nc_low VALUES LESS THAN (1000)

  , SUBPARTITION p_nc_average VALUES LESS THAN (10000)

  , SUBPARTITION p_nc_high VALUES LESS THAN (100000)

  , SUBPARTITION p_nc_extraordinary VALUES LESS THAN (MAXVALUE)

  )

, PARTITION p_southcentral VALUES ('OK', 'TX')

  ( SUBPARTITION p_sc_low VALUES LESS THAN (1000)

  , SUBPARTITION p_sc_average VALUES LESS THAN (10000)

  , SUBPARTITION p_sc_high VALUES LESS THAN (100000)

  , SUBPARTITION p_sc_extraordinary VALUES LESS THAN (MAXVALUE)

  )

) ENABLE ROW MOVEMENT;

To learn how using a subpartition template can simplify the specification of a composite partitioned table, see "Using Subpartition Templates to Describe Composite Partitioned Tables".

Creating Composite Interval-* Partitioned Tables

The concepts of interval-* composite partitioning are similar to the concepts for range-* partitioning. However, you extend the PARTITION BY RANGE clause to include the INTERVAL definition. You must specify at least one range partition using the PARTITION clause. The range partitioning key value determines the high value of the range partitions, which is called the transition point, and the database automatically creates interval partitions for data beyond that transition point.

The subpartitions for intervals in an interval-* partitioned table will be created when the database creates the interval. You can specify the definition of future subpartitions only through the use of a subpartition template. To learn more about how to use a subpartition template, see "Using Subpartition Templates to Describe Composite Partitioned Tables".

Creating Composite Interval-Hash Partitioned Tables

You can create an interval-hash partitioned table with multiple hash partitions using one of the following methods:

  • Specify a number of hash partitions in the PARTITIONS clause.

  • Use a subpartition template.

If you do not use either of these methods, then future interval partitions will only get a single hash subpartition.

The following example shows the sales table, interval partitioned using monthly intervals on time_id, with hash subpartitions by cust_id. Note that this example specifies a number of hash partitions, without any specific tablespace assignment to the individual hash partitions.

CREATE TABLE sales

  ( prod_id       NUMBER(6)

  , cust_id       NUMBER

  , time_id       DATE

  , channel_id    CHAR(1)

  , promo_id      NUMBER(6)

  , quantity_sold NUMBER(3)

  , amount_sold   NUMBER(10,2)

  )

 PARTITION BY RANGE (time_id) INTERVAL (NUMTOYMINTERVAL(1,'MONTH'))

 SUBPARTITION BY HASH (cust_id) SUBPARTITIONS 4

 ( PARTITION before_2000 VALUES LESS THAN (TO_DATE('01-JAN-2000','dd-MON-yyyy')))

PARALLEL;

The following example shows the same sales table, interval partitioned using monthly intervals on time_id, again with hash subpartitions by cust_id. This time, however, individual hash partitions will be stored in separate tablespaces. Note that the subpartition template is used in order to define the tablespace assignment for future hash subpartitions. To learn more about how to use a subpartition template, see "Using Subpartition Templates to Describe Composite Partitioned Tables".

CREATE TABLE sales

  ( prod_id       NUMBER(6)

  , cust_id       NUMBER

  , time_id       DATE

  , channel_id    CHAR(1)

  , promo_id      NUMBER(6)

  , quantity_sold NUMBER(3)

  , amount_sold   NUMBER(10,2)

  )

 PARTITION BY RANGE (time_id) INTERVAL (NUMTOYMINTERVAL(1,'MONTH'))

 SUBPARTITION BY hash(cust_id)

   SUBPARTITION template

   ( SUBPARTITION p1 TABLESPACE ts1

   , SUBPARTITION p2 TABLESPACE ts2

   , SUBPARTITION p3 TABLESPACE ts3

   , SUBPARTITION P4 TABLESPACE ts4

   )

 ( PARTITION before_2000 VALUES LESS THAN (TO_DATE('01-JAN-2000','dd-MON-yyyy'))

) PARALLEL;

Creating Composite Interval-List Partitioned Tables

The only way to define list subpartitions for future interval partitions is through the use of the subpartition template. If you do not use the subpartitioning template, then the only subpartition that will be created for every interval partition is a DEFAULT subpartition. To learn more about how to use a subpartition template, see "Using Subpartition Templates to Describe Composite Partitioned Tables".

The following example shows the sales table, interval partitioned using daily intervals on time_id, with list subpartitions by channel_id.

CREATE TABLE sales

  ( prod_id       NUMBER(6)

  , cust_id       NUMBER

  , time_id       DATE

  , channel_id    CHAR(1)

  , promo_id      NUMBER(6)

  , quantity_sold NUMBER(3)

  , amount_sold   NUMBER(10,2)

  )

 PARTITION BY RANGE (time_id) INTERVAL (NUMTODSINTERVAL(1,'DAY'))

SUBPARTITION BY RANGE(amount_sold)

   SUBPARTITION TEMPLATE

   ( SUBPARTITION p_low VALUES LESS THAN (1000)

   , SUBPARTITION p_medium VALUES LESS THAN (4000)

   , SUBPARTITION p_high VALUES LESS THAN (8000)

   , SUBPARTITION p_ultimate VALUES LESS THAN (maxvalue)

   )

 ( PARTITION before_2000 VALUES LESS THAN (TO_DATE('01-JAN-2000','dd-MON-yyyy')))

PARALLEL;

Creating Composite Interval-Range Partitioned Tables

The only way to define range subpartitions for future interval partitions is through the use of the subpartition template. If you do not use the subpartition template, then the only subpartition that will be created for every interval partition is a range subpartition with the MAXVALUE upper boundary. To learn more about how to use a subpartition template, see "Using Subpartition Templates to Describe Composite Partitioned Tables".

The following example shows the sales table, interval partitioned using daily intervals on time_id, with range subpartitions by amount_sold.

CREATE TABLE sales

  ( prod_id       NUMBER(6)

  , cust_id       NUMBER

  , time_id       DATE

  , channel_id    CHAR(1)

  , promo_id      NUMBER(6)

  , quantity_sold NUMBER(3)

  , amount_sold   NUMBER(10,2)

  )

 PARTITION BY RANGE (time_id) INTERVAL (NUMTODSINTERVAL(1,'DAY'))

 SUBPARTITION BY LIST (channel_id)

   SUBPARTITION TEMPLATE

   ( SUBPARTITION p_catalog VALUES ('C')

   , SUBPARTITION p_internet VALUES ('I')

   , SUBPARTITION p_partners VALUES ('P')

   , SUBPARTITION p_direct_sales VALUES ('S')

   , SUBPARTITION p_tele_sales VALUES ('T')

   )

 ( PARTITION before_2000 VALUES LESS THAN (TO_DATE('01-JAN-2000','dd-MON-yyyy')))

PARALLEL;

Using Subpartition Templates to Describe Composite Partitioned Tables

You can create subpartitions in a composite partitioned table using a subpartition template. A subpartition template simplifies the specification of subpartitions by not requiring that a subpartition descriptor be specified for every partition in the table. Instead, you describe subpartitions only once in a template, then apply that subpartition template to every partition in the table. For interval-* composite partitioned tables, the subpartition template is the only way to define subpartitions for interval partitions.

The subpartition template is used whenever a subpartition descriptor is not specified for a partition. If a subpartition descriptor is specified, then it is used instead of the subpartition template for that partition. If no subpartition template is specified, and no subpartition descriptor is supplied for a partition, then a single default subpartition is created.

Specifying a Subpartition Template for a *-Hash Partitioned Table

In the case of [range | interval | list]-hash partitioned tables, the subpartition template can describe the subpartitions in detail, or it can specify just the number of hash subpartitions.

The following example creates a range-hash partitioned table using a subpartition template:

CREATE TABLE emp_sub_template (deptno NUMBER, empname VARCHAR(32), grade NUMBER)

     PARTITION BY RANGE(deptno) SUBPARTITION BY HASH(empname)

     SUBPARTITION TEMPLATE

         (SUBPARTITION a TABLESPACE ts1,

          SUBPARTITION b TABLESPACE ts2,

          SUBPARTITION c TABLESPACE ts3,

          SUBPARTITION d TABLESPACE ts4

         )

    (PARTITION p1 VALUES LESS THAN (1000),

     PARTITION p2 VALUES LESS THAN (2000),

     PARTITION p3 VALUES LESS THAN (MAXVALUE)

    );

This example produces the following table description:

  • Every partition has four subpartitions as described in the subpartition template.

  • Each subpartition has a tablespace specified. It is required that if a tablespace is specified for one subpartition in a subpartition template, then one must be specified for all.

  • The names of the subpartitions, unless you use interval-* subpartitioning, are generated by concatenating the partition name with the subpartition name in the form:

    partition name_subpartition name

    For interval-* subpartitioning, the subpartition names are system-generated in the form:

    SYS_SUBPn

The following query displays the subpartition names and tablespaces:

SQL> SELECT TABLESPACE_NAME, PARTITION_NAME, SUBPARTITION_NAME

  2  FROM DBA_TAB_SUBPARTITIONS WHERE TABLE_NAME='EMP_SUB_TEMPLATE'

  3  ORDER BY TABLESPACE_NAME;


TABLESPACE_NAME PARTITION_NAME  SUBPARTITION_NAME

--------------- --------------- ------------------

TS1             P1              P1_A

TS1             P2              P2_A

TS1             P3              P3_A

TS2             P1              P1_B

TS2             P2              P2_B

TS2             P3              P3_B

TS3             P1              P1_C

TS3             P2              P2_C

TS3             P3              P3_C

TS4             P1              P1_D

TS4             P2              P2_D

TS4             P3              P3_D


12 rows selected.

Specifying a Subpartition Template for a *-List Partitioned Table

The following example, for a range-list partitioned table, illustrates how using a subpartition template can help you stripe data across tablespaces. In this example a table is created where the table subpartitions are vertically striped, meaning that subpartition n from every partition is in the same tablespace.

CREATE TABLE stripe_regional_sales

            ( deptno number, item_no varchar2(20),

              txn_date date, txn_amount number, state varchar2(2))

   PARTITION BY RANGE (txn_date)

   SUBPARTITION BY LIST (state)

   SUBPARTITION TEMPLATE 

      (SUBPARTITION northwest VALUES ('OR', 'WA') TABLESPACE tbs_1,

       SUBPARTITION southwest VALUES ('AZ', 'UT', 'NM') TABLESPACE tbs_2,

       SUBPARTITION northeast VALUES ('NY', 'VM', 'NJ') TABLESPACE tbs_3,

       SUBPARTITION southeast VALUES ('FL', 'GA') TABLESPACE tbs_4,

       SUBPARTITION midwest VALUES ('SD', 'WI') TABLESPACE tbs_5,

       SUBPARTITION south VALUES ('AL', 'AK') TABLESPACE tbs_6,

       SUBPARTITION others VALUES (DEFAULT ) TABLESPACE tbs_7

      )

  (PARTITION q1_1999 VALUES LESS THAN ( TO_DATE('01-APR-1999','DD-MON-YYYY')),

   PARTITION q2_1999 VALUES LESS THAN ( TO_DATE('01-JUL-1999','DD-MON-YYYY')),

   PARTITION q3_1999 VALUES LESS THAN ( TO_DATE('01-OCT-1999','DD-MON-YYYY')),

   PARTITION q4_1999 VALUES LESS THAN ( TO_DATE('1-JAN-2000','DD-MON-YYYY'))

  );

If you specified the tablespaces at the partition level (for example, tbs_1 for partition q1_1999, tbs_2 for partition q2_1999, tbs_3 for partition q3_1999, and tbs_4 for partition q4_1999) and not in the subpartition template, then the table would be horizontally striped. All subpartitions would be in the tablespace of the owning partition.

Using Multicolumn Partitioning Keys

For range-partitioned and hash-partitioned tables, you can specify up to 16 partitioning key columns. Multicolumn partitioning should be used when the partitioning key is composed of several columns and subsequent columns define a higher granularity than the preceding ones. The most common scenario is a decomposed DATE or TIMESTAMP key, consisting of separated columns, for year, month, and day.

In evaluating multicolumn partitioning keys, the database uses the second value only if the first value cannot uniquely identify a single target partition, and uses the third value only if the first and second do not determine the correct partition, and so forth. A value cannot determine the correct partition only when a partition bound exactly matches that value and the same bound is defined for the next partition. The nth column will therefore be investigated only when all previous (n-1) values of the multicolumn key exactly match the (n-1) bounds of a partition. A second column, for example, will be evaluated only if the first column exactly matches the partition boundary value. If all column values exactly match all of the bound values for a partition, then the database will determine that the row does not fit in this partition and will consider the next partition for a match.

In the case of nondeterministic boundary definitions (successive partitions with identical values for at least one column), the partition boundary value becomes an inclusive value, representing a "less than or equal to" boundary. This is in contrast to deterministic boundaries, where the values are always regarded as "less than" boundaries.

The following example illustrates the column evaluation for a multicolumn range-partitioned table, storing the actual DATE information in three separate columns: year, month, and day. The partitioning granularity is a calendar quarter. The partitioned table being evaluated is created as follows:

CREATE TABLE sales_demo (

   year          NUMBER, 

   month         NUMBER,

   day           NUMBER,

   amount_sold   NUMBER) 

PARTITION BY RANGE (year,month) 

  (PARTITION before2001 VALUES LESS THAN (2001,1),

   PARTITION q1_2001    VALUES LESS THAN (2001,4),

   PARTITION q2_2001    VALUES LESS THAN (2001,7),

   PARTITION q3_2001    VALUES LESS THAN (2001,10),

   PARTITION q4_2001    VALUES LESS THAN (2002,1),

   PARTITION future     VALUES LESS THAN (MAXVALUE,0));


REM  12-DEC-2000

INSERT INTO sales_demo VALUES(2000,12,12, 1000);

REM  17-MAR-2001

INSERT INTO sales_demo VALUES(2001,3,17, 2000);

REM  1-NOV-2001

INSERT INTO sales_demo VALUES(2001,11,1, 5000);

REM  1-JAN-2002

INSERT INTO sales_demo VALUES(2002,1,1, 4000);

The year value for 12-DEC-2000 satisfied the first partition, before2001, so no further evaluation is needed:

SELECT * FROM sales_demo PARTITION(before2001);


      YEAR      MONTH        DAY AMOUNT_SOLD

---------- ---------- ---------- -----------

      2000         12         12        1000

The information for 17-MAR-2001 is stored in partition q1_2001. The first partitioning key column, year, does not by itself determine the correct partition, so the second partitioning key column, month, must be evaluated.

SELECT * FROM sales_demo PARTITION(q1_2001);


      YEAR      MONTH        DAY AMOUNT_SOLD

---------- ---------- ---------- -----------

      2001          3         17        2000

Following the same determination rule as for the previous record, the second column, month, determines partition q4_2001 as correct partition for 1-NOV-2001:

SELECT * FROM sales_demo PARTITION(q4_2001);


      YEAR      MONTH        DAY AMOUNT_SOLD

---------- ---------- ---------- -----------

      2001         11          1        5000

The partition for 01-JAN-2002 is determined by evaluating only the year column, which indicates the future partition:

SELECT * FROM sales_demo PARTITION(future);


      YEAR      MONTH        DAY AMOUNT_SOLD

---------- ---------- ---------- -----------

      2002          1          1        4000

If the database encounters MAXVALUE in one of the partitioning key columns, then all other values of subsequent columns become irrelevant. That is, a definition of partition future in the preceding example, having a bound of (MAXVALUE,0) is equivalent to a bound of (MAXVALUE,100) or a bound of (MAXVALUE,MAXVALUE).

The following example illustrates the use of a multicolumn partitioned approach for table supplier_parts, storing the information about which suppliers deliver which parts. To distribute the data in equal-sized partitions, it is not sufficient to partition the table based on the supplier_id, because some suppliers might provide hundreds of thousands of parts, while others provide only a few specialty parts. Instead, you partition the table on (supplier_id, partnum) to manually enforce equal-sized partitions.

CREATE TABLE supplier_parts (

   supplier_id      NUMBER, 

   partnum          NUMBER,

   price            NUMBER)

PARTITION BY RANGE (supplier_id, partnum)

  (PARTITION p1 VALUES LESS THAN  (10,100),

   PARTITION p2 VALUES LESS THAN (10,200),

   PARTITION p3 VALUES LESS THAN (MAXVALUE,MAXVALUE));

The following three records are inserted into the table:

INSERT INTO supplier_parts VALUES (5,5, 1000);

INSERT INTO supplier_parts VALUES (5,150, 1000);

INSERT INTO supplier_parts VALUES (10,100, 1000);

The first two records are inserted into partition p1, uniquely identified by supplier_id. However, the third record is inserted into partition p2; it matches all range boundary values of partition p1 exactly and the database therefore considers the following partition for a match. The value of partnum satisfies the criteria < 200, so it is inserted into partition p2.

SELECT * FROM supplier_parts PARTITION (p1);


SUPPLIER_ID    PARTNUM      PRICE

----------- ---------- ----------

          5          5       1000

          5        150       1000


SELECT * FROM supplier_parts PARTITION (p2);


SUPPLIER_ID    PARTNUM      PRICE

----------- ---------- ----------

          10       100       1000

Every row with supplier_id < 10 will be stored in partition p1, regardless of the partnum value. The column partnum will be evaluated only if supplier_id =10, and the corresponding rows will be inserted into partition p1, p2, or even into p3 when partnum >=200. To achieve equal-sized partitions for ranges of supplier_parts, you could choose a composite range-hash partitioned table, range partitioned by supplier_id, hash subpartitioned by partnum.

Defining the partition boundaries for multicolumn partitioned tables must obey some rules. For example, consider a table that is range partitioned on three columns a, b, and c. The individual partitions have range values represented as follows:

P0(a0, b0, c0)

P1(a1, b1, c1)

P2(a2, b2, c2)

...

Pn(an, bn, cn)

The range values you provide for each partition must follow these rules:

  • a0 must be less than or equal to a1, and a1 must be less than or equal to a2, and so on.

  • If a0=a1, then b0 must be less than or equal to b1. If a0 < a1, then b0 and b1 can have any values. If a0=a1 and b0=b1, then c0 must be less than or equal to c1. If b0<b1, then c0 and c1 can have any values, and so on.

  • If a1=a2, then b1 must be less than or equal to b2. If a1<a2, then b1 and b2 can have any values. If a1=a2 and b1=b2, then c1 must be less than or equal to c2. If b1<b2, then c1 and c2 can have any values, and so on.

Using Virtual Column-Based Partitioning

In the context of partitioning, a virtual column can be used as any regular column. All partition methods are supported when using virtual columns, including interval partitioning and all different combinations of composite partitioning. A virtual column that you want to use as the partitioning column cannot use calls to a PL/SQL function.

See Also:

Oracle Database SQL Language Reference for the syntax on how to create a virtual column

The following example shows the sales table partitioned by range-range using a virtual column for the subpartitioning key. The virtual column calculates the total value of a sale by multiplying amount_sold and quantity_sold.

CREATE TABLE sales

  ( prod_id       NUMBER(6) NOT NULL

  , cust_id       NUMBER NOT NULL

  , time_id       DATE NOT NULL

  , channel_id    CHAR(1) NOT NULL

  , promo_id      NUMBER(6) NOT NULL

  , quantity_sold NUMBER(3) NOT NULL

  , amount_sold   NUMBER(10,2) NOT NULL

  , total_amount AS (quantity_sold * amount_sold)

  )

 PARTITION BY RANGE (time_id) INTERVAL (NUMTOYMINTERVAL(1,'MONTH'))

 SUBPARTITION BY RANGE(total_amount)

 SUBPARTITION TEMPLATE

   ( SUBPARTITION p_small VALUES LESS THAN (1000)

   , SUBPARTITION p_medium VALUES LESS THAN (5000)

   , SUBPARTITION p_large VALUES LESS THAN (10000)

   , SUBPARTITION p_extreme VALUES LESS THAN (MAXVALUE)

   )

 (PARTITION sales_before_2007 VALUES LESS THAN

        (TO_DATE('01-JAN-2007','dd-MON-yyyy'))

)

ENABLE ROW MOVEMENT

PARALLEL NOLOGGING;

As the example shows, row movement is also supported with virtual columns. If row movement is enabled, then a row will migrate from one partition to another partition if the virtual column evaluates to a value that belongs to another partition.

Using Table Compression with Partitioned Tables

For heap-organized partitioned tables, you can compress some or all partitions using table compression. The compression attribute can be declared for a tablespace, a table, or a partition of a table. Whenever the compress attribute is not specified, it is inherited like any other storage attribute.

The following example creates a list-partitioned table with one compressed partition costs_old. The compression attribute for the table and all other partitions is inherited from the tablespace level.

CREATE TABLE costs_demo (

   prod_id     NUMBER(6),    time_id     DATE, 

   unit_cost   NUMBER(10,2), unit_price  NUMBER(10,2))

PARTITION BY RANGE (time_id)

   (PARTITION costs_old 

       VALUES LESS THAN (TO_DATE('01-JAN-2003', 'DD-MON-YYYY')) COMPRESS,

    PARTITION costs_q1_2003 

       VALUES LESS THAN (TO_DATE('01-APR-2003', 'DD-MON-YYYY')),

    PARTITION costs_q2_2003

       VALUES LESS THAN (TO_DATE('01-JUN-2003', 'DD-MON-YYYY')),

    PARTITION costs_recent VALUES LESS THAN (MAXVALUE));

Using Key Compression with Partitioned Indexes

You can compress some or all partitions of a B-tree index using key compression. Key compression is applicable only to B-tree indexes. Bitmap indexes are stored in a compressed manner by default. An index using key compression eliminates repeated occurrences of key column prefix values, thus saving space and I/O.

The following example creates a local partitioned index with all partitions except the most recent one compressed:

CREATE INDEX i_cost1 ON costs_demo (prod_id) COMPRESS LOCAL

   (PARTITION costs_old, PARTITION costs_q1_2003, 

    PARTITION costs_q2_2003, PARTITION costs_recent NOCOMPRESS);

You cannot specify COMPRESS (or NOCOMPRESS) explicitly for an index subpartition. All index subpartitions of a given partition inherit the key compression setting from the parent partition.

To modify the key compression attribute for all subpartitions of a given partition, you must first issue an ALTER INDEX...MODIFY PARTITION statement and then rebuild all subpartitions. The MODIFY PARTITION clause will mark all index subpartitions as UNUSABLE.

Creating Partitioned Index-Organized Tables

For index-organized tables, you can use the range, list, or hash partitioning method. The semantics for creating partitioned index-organized tables is similar to that for regular tables with these differences:

  • When you create the table, you specify the ORGANIZATION INDEX clause, and INCLUDING and OVERFLOW clauses as necessary.

  • The PARTITION or PARTITIONS clauses can have OVERFLOW subclauses that allow you to specify attributes of the overflow segments at the partition level.

Specifying an OVERFLOW clause results in the overflow data segments themselves being equipartitioned with the primary key index segments. Thus, for partitioned index-organized tables with overflow, each partition has an index segment and an overflow data segment.

For index-organized tables, the set of partitioning columns must be a subset of the primary key columns. Because rows of an index-organized table are stored in the primary key index for the table, the partitioning criterion has an effect on the availability. By choosing the partitioning key to be a subset of the primary key, an insert operation only needs to verify uniqueness of the primary key in a single partition, thereby maintaining partition independence.

Support for secondary indexes on index-organized tables is similar to the support for regular tables. Because of the logical nature of the secondary indexes, global indexes on index-organized tables remain usable for certain operations where they would be marked UNUSABLE for regular tables.

See Also:

Creating Range-Partitioned Index-Organized Tables

You can partition index-organized tables, and their secondary indexes, by the range method. In the following example, a range-partitioned index-organized table sales is created. The INCLUDING clause specifies that all columns after week_no are to be stored in an overflow segment. There is one overflow segment for each partition, all stored in the same tablespace (overflow_here). Optionally, OVERFLOW TABLESPACE could be specified at the individual partition level, in which case some or all of the overflow segments could have separate TABLESPACE attributes.

CREATE TABLE sales(acct_no NUMBER(5), 

                   acct_name CHAR(30), 

                   amount_of_sale NUMBER(6), 

                   week_no INTEGER,

                   sale_details VARCHAR2(1000),

             PRIMARY KEY (acct_no, acct_name, week_no)) 

     ORGANIZATION INDEX 

             INCLUDING week_no

             OVERFLOW TABLESPACE overflow_here

     PARTITION BY RANGE (week_no)

            (PARTITION VALUES LESS THAN (5) 

                   TABLESPACE ts1,

             PARTITION VALUES LESS THAN (9) 

                   TABLESPACE ts2 OVERFLOW TABLESPACE overflow_ts2,

             ...

             PARTITION VALUES LESS THAN (MAXVALUE) 

                   TABLESPACE ts13);

Creating Hash-Partitioned Index-Organized Tables

Another option for partitioning index-organized tables is to use the hash method. In the following example, the sales index-organized table is partitioned by the hash method.

CREATE TABLE sales(acct_no NUMBER(5), 

                   acct_name CHAR(30), 

                   amount_of_sale NUMBER(6), 

                   week_no INTEGER,

                   sale_details VARCHAR2(1000),

             PRIMARY KEY (acct_no, acct_name, week_no)) 

     ORGANIZATION INDEX 

             INCLUDING week_no

     OVERFLOW

          PARTITION BY HASH (week_no)

             PARTITIONS 16

             STORE IN (ts1, ts2, ts3, ts4)

             OVERFLOW STORE IN (ts3, ts6, ts9);

Note:

A well-designed hash function is intended to distribute rows in a well-balanced fashion among the partitions. Therefore, updating the primary key column(s) of a row is very likely to move that row to a different partition. Oracle recommends that you explicitly specify the ENABLE ROW MOVEMENT clause when creating a hash-partitioned index-organized table with a changeable partitioning key. The default is that ENABLE ROW MOVEMENT is disabled.

Creating List-Partitioned Index-Organized Tables

The other option for partitioning index-organized tables is to use the list method. In the following example, the sales index-organized table is partitioned by the list method. This example uses the example tablespace, which is part of the sample schemas in your seed database. Normally you would specify different tablespace storage for different partitions.

CREATE TABLE sales(acct_no NUMBER(5), 

                   acct_name CHAR(30), 

                   amount_of_sale NUMBER(6), 

                   week_no INTEGER,

                   sale_details VARCHAR2(1000),

             PRIMARY KEY (acct_no, acct_name, week_no)) 

     ORGANIZATION INDEX 

             INCLUDING week_no

             OVERFLOW TABLESPACE example

     PARTITION BY LIST (week_no)

            (PARTITION VALUES (1, 2, 3, 4) 

                   TABLESPACE example,

             PARTITION VALUES (5, 6, 7, 8) 

                   TABLESPACE example OVERFLOW TABLESPACE example,

             PARTITION VALUES (DEFAULT) 

                   TABLESPACE example);

Partitioning Restrictions for Multiple Block Sizes

Use caution when creating partitioned objects in a database with tablespaces of different block sizes. The storage of partitioned objects in such tablespaces is subject to some restrictions. Specifically, all partitions of the following entities must reside in tablespaces of the same block size:

  • Conventional tables

  • Indexes

  • Primary key index segments of index-organized tables

  • Overflow segments of index-organized tables

  • LOB columns stored out of line

Therefore:

  • For each conventional table, all partitions of that table must be stored in tablespaces with the same block size.

  • For each index-organized table, all primary key index partitions must reside in tablespaces of the same block size, and all overflow partitions of that table must reside in tablespaces of the same block size. However, index partitions and overflow partitions can reside in tablespaces of different block size.

  • For each index (global or local), each partition of that index must reside in tablespaces of the same block size. However, partitions of different indexes defined on the same object can reside in tablespaces of different block sizes.

  • For each LOB column, each partition of that column must be stored in tablespaces of equal block sizes. However, different LOB columns can be stored in tablespaces of different block sizes.

When you create or alter a partitioned table or index, all tablespaces you explicitly specify for the partitions and subpartitions of each entity must be of the same block size. If you do not explicitly specify tablespace storage for an entity, the tablespaces the database uses by default must be of the same block size. Therefore you must be aware of the default tablespaces at each level of the partitioned object.

Maintaining Partitions

This section describes how to perform partition and subpartition maintenance operations for both tables and indexes.

Table 3-1 lists partition maintenance operations that can be performed on partitioned tables and composite partitioned tables, and Table 3-2 lists subpartition maintenance operations that can be performed on composite partitioned tables. For each type of partitioning and subpartitioning, the specific clause of the ALTER TABLE statement that is used to perform that maintenance operation is listed.

Table 3-1 ALTER TABLE Maintenance Operations for Table Partitions

Maintenance Operation Range Composite Range-* Interval Composite Interval-* Hash List Composite List-* Reference

Adding Partitions

ADD PARTITION

ADD PARTITION

ADD PARTITION

ADD PARTITION

N/AFoot 1 

Coalescing Partitions

N/A

N/A

COALESCE PARTITION

N/A

N/AFootref 1

Dropping Partitions

DROP PARTITION

DROP PARTITION

N/A

DROP PARTITION

N/AFootref 1

Exchanging Partitions

EXCHANGE PARTITION

EXCHANGE PARTITION

EXCHANGE PARTITION

EXCHANGE PARTITION

EXCHANGE PARTITION

Merging Partitions

MERGE PARTITIONS

MERGE PARTITIONS

N/A

MERGE PARTITIONS

N/AFootref 1

Modifying Default Attributes

MODIFY DEFAULT ATTRIBUTES

MODIFY DEFAULT ATTRIBUTES

MODIFY DEFAULT ATTRIBUTES

MODIFY DEFAULT ATTRIBUTES

MODIFY DEFAULT ATTRIBUTES

Modifying Real Attributes of Partitions

MODIFY PARTITION

MODIFY PARTITION

MODIFY PARTITION

MODIFY PARTITION

MODIFY PARTITION

Modifying List Partitions: Adding Values

N/A

N/A

N/A

MODIFY PARTITION ... ADD VALUES

N/A

Modifying List Partitions: Dropping Values

N/A

N/A

N/A

MODIFY PARTITION ... DROP VALUES

N/A

Moving Partitions

MOVE PARTITION

MOVE PARTITION

MOVE PARTITION

MOVE PARTITION

MOVE PARTITION

Renaming Partitions

RENAME PARTITION

RENAME PARTITION

RENAME PARTITION

RENAME PARTITION

RENAME PARTITION

Splitting Partitions

SPLIT PARTITION

SPLIT PARTITION

N/A

SPLIT PARTITION

N/AFootref 1

Truncating Partitions

TRUNCATE PARTITION

TRUNCATE PARTITION

TRUNCATE PARTITION

TRUNCATE PARTITION

TRUNCATE PARTITION


Footnote 1 These operations cannot be performed on reference-partitioned tables. If performed on a parent table, then these operations will cascade to all descendant tables.

Table 3-2 ALTER TABLE Maintenance Operations for Table Subpartitions

Maintenance Operation Composite *-Range Composite *-Hash Composite *-List

Adding Partitions

MODIFY PARTITION ... ADD SUBPARTITION

MODIFY PARTITION ... ADD SUBPARTITION

MODIFY PARTITION ... ADD SUBPARTITION

Coalescing Partitions

N/A

MODIFY PARTITION ... COALESCE SUBPARTITION

N/A

Dropping Partitions

DROP SUBPARTITION

N/A

DROP SUBPARTITION

Exchanging Partitions

EXCHANGE SUBPARTITION

N/A

EXCHANGE SUBPARTITION

Merging Partitions

MERGE SUBPARTITIONS

N/A

MERGE SUBPARTITIONS

Modifying Default Attributes

MODIFY DEFAULT ATTRIBUTES FOR PARTITION

MODIFY DEFAULT ATTRIBUTES FOR PARTITION

MODIFY DEFAULT ATTRIBUTES FOR PARTITION

Modifying Real Attributes of Partitions

MODIFY SUBPARTITION

MODIFY SUBPARTITION

MODIFY SUBPARTITION

Modifying List Partitions: Adding Values

N/A

N/A

MODIFY SUBPARTITION ... ADD VALUES

Modifying List Partitions: Dropping Values

N/A

N/A

MODIFY SUBPARTITION ... DROP VALUES

Modifying a Subpartition Template

SET SUBPARTITION TEMPLATE

SET SUBPARTITION TEMPLATE

SET SUBPARTITION TEMPLATE

Moving Partitions

MOVE SUBPARTITION

MOVE SUBPARTITION

MOVE SUBPARTITION

Renaming Partitions

RENAME SUBPARTITION

RENAME SUBPARTITION

RENAME SUBPARTITION

Splitting Partitions

SPLIT SUBPARTITION

N/A

SPLIT SUBPARTITION

Truncating Partitions

TRUNCATE SUBPARTITION

TRUNCATE SUBPARTITION

TRUNCATE SUBPARTITION


Note:

The first time you use table compression to introduce a compressed partition into a partitioned table that has bitmap indexes and that currently contains only uncompressed partitions, you must do the following:
  • Either drop all existing bitmap indexes and bitmap index partitions, or mark them UNUSABLE.

  • Set the table compression attribute.

  • Rebuild the indexes.

These actions are independent of whether any partitions contain data and of the operation that introduces the compressed partition.

This does not apply to partitioned tables with B-tree indexes or to partitioned index-organized tables.

Table 3-3 lists maintenance operations that can be performed on index partitions, and indicates on which type of index (global or local) they can be performed. The ALTER INDEX clause used for the maintenance operation is shown.

Global indexes do not reflect the structure of the underlying table. If partitioned, they can be partitioned by range or hash. Partitioned global indexes share some, but not all, of the partition maintenance operations that can be performed on partitioned tables.

Because local indexes reflect the underlying structure of the table, partitioning is maintained automatically when table partitions and subpartitions are affected by maintenance activity. Therefore, partition maintenance on local indexes is less necessary and there are fewer options.

Table 3-3 ALTER INDEX Maintenance Operations for Index Partitions

Maintenance Operation Type of Index Type of Index Partitioning
Range Hash and List Composite

Adding Index Partitions

Global

-

ADD PARTITION (hash only)

-

 

Local

N/A

N/A

N/A

Dropping Index Partitions

Global

DROP PARTITION

-

-

 

Local

N/A

N/A

N/A

Modifying Default Attributes of Index Partitions

Global

MODIFY DEFAULT ATTRIBUTES

-

-

 

Local

MODIFY DEFAULT ATTRIBUTES

MODIFY DEFAULT ATTRIBUTES

MODIFY DEFAULT ATTRIBUTES

MODIFY DEFAULT ATTRIBUTES FOR PARTITION

Modifying Real Attributes of Index Partitions

Global

MODIFY PARTITION

-

-

 

Local

MODIFY PARTITION

MODIFY PARTITION

MODIFY PARTITION

MODIFY SUBPARTITION

Rebuilding Index Partitions

Global

REBUILD PARTITION

-

-

 

Local

REBUILD PARTITION

REBUILD PARTITION

REBUILD SUBPARTITION

Renaming Index Partitions

Global

RENAME PARTITION

-

-

 

Local

RENAME PARTITION

RENAME PARTITION

RENAME PARTITION

RENAME SUBPARTITION

Splitting Index Partitions

Global

SPLIT PARTITION

-

-

 

Local

N/A

N/A

N/A


Note:

The following sections discuss maintenance operations on partitioned tables. Where the usability of indexes or index partitions affected by the maintenance operation is discussed, consider the following:
  • Only indexes and index partitions that are not empty are candidates for being marked UNUSABLE. If they are empty, the USABLE/UNUSABLE status is left unchanged.

  • Only indexes or index partitions with USABLE status are updated by subsequent DML.

Updating Indexes Automatically

Before discussing the individual maintenance operations for partitioned tables and indexes, it is important to discuss the effects of the UPDATE INDEXES clause that can be specified in the ALTER TABLE statement.

By default, many table maintenance operations on partitioned tables invalidate (mark UNUSABLE) the corresponding indexes or index partitions. You must then rebuild the entire index or, in the case of a global index, each of its partitions. The database lets you override this default behavior if you specify UPDATE INDEXES in your ALTER TABLE statement for the maintenance operation. Specifying this clause tells the database to update the index at the time it executes the maintenance operation DDL statement. This provides the following benefits:

  • The index is updated in conjunction with the base table operation. You are not required to later and independently rebuild the index.

  • The index is more highly available, because it does not get marked UNUSABLE. The index remains available even while the partition DDL is executing and it can be used to access unaffected partitions in the table.

  • You need not look up the names of all invalid indexes to rebuild them.

Optional clauses for local indexes let you specify physical and storage characteristics for updated local indexes and their partitions.

  • You can specify physical attributes, tablespace storage, and logging for each partition of each local index. Alternatively, you can specify only the PARTITION keyword and let the database update the partition attributes as follows:

    • For operations on a single table partition (such as MOVE PARTITION and SPLIT PARTITION), the corresponding index partition inherits the attributes of the affected index partition. The database does not generate names for new index partitions, so any new index partitions resulting from this operation inherit their names from the corresponding new table partition.

    • For MERGE PARTITION operations, the resulting local index partition inherits its name from the resulting table partition and inherits its attributes from the local index.

  • For a composite-partitioned index, you can specify tablespace storage for each subpartition.

See Also:

the update_all_indexes_clause of ALTER TABLE for the syntax for updating indexes

The following operations support the UPDATE INDEXES clause:

  • ADD PARTITION | SUBPARTITION

  • COALESCE PARTITION | SUBPARTITION

  • DROP PARTITION | SUBPARTITION

  • EXCHANGE PARTITION | SUBPARTITION

  • MERGE PARTITION | SUBPARTITION

  • MOVE PARTITION | SUBPARTITION

  • SPLIT PARTITION | SUBPARTITION

  • TRUNCATE PARTITION | SUBPARTITION

SKIP_UNUSABLE_INDEXES Initialization Parameter

SKIP_UNUSABLE_INDEXES is an initialization parameter with a default value of TRUE. This setting disables error reporting of indexes and index partitions marked UNUSABLE. If you do not want the database to choose an alternative execution plan to avoid the unusable elements, then you should set this parameter to FALSE.

Considerations when Updating Indexes Automatically

The following implications are worth noting when you specify UPDATE INDEXES:

  • The partition DDL statement takes longer to execute, because indexes that were previously marked UNUSABLE are updated. However, you must compare this increase with the time it takes to execute DDL without updating indexes, and then rebuild all indexes. A rule of thumb is that it is faster to update indexes if the size of the partition is less that 5% of the size of the table.

  • The DROP, TRUNCATE, and EXCHANGE operations are no longer fast operations. Again, you must compare the time it takes to do the DDL and then rebuild all indexes.

  • When you update a table with a global index:

    • The index is updated in place. The updates to the index are logged, and redo and undo records are generated. In contrast, if you rebuild an entire global index, you can do so in NOLOGGING mode.

    • Rebuilding the entire index manually creates a more efficient index, because it is more compact with space better utilized.

  • The UPDATE INDEXES clause is not supported for index-organized tables. However, the UPDATE GLOBAL INDEXES clause may be used with DROP PARTITION, TRUNCATE PARTITION, and EXCHANGE PARTITION operations to keep the global indexes on index-organized tables usable. For the remaining operations in the above list, global indexes on index-organized tables remain usable. In addition, local index partitions on index-organized tables remain usable after a MOVE PARTITION operation.

Adding Partitions

This section describes how to manually add new partitions to a partitioned table and explains why partitions cannot be specifically added to most partitioned indexes.

Adding a Partition to a Range-Partitioned Table

Use the ALTER TABLE ... ADD PARTITION statement to add a new partition to the "high" end (the point after the last existing partition). To add a partition at the beginning or in the middle of a table, use the SPLIT PARTITION clause.

For example, consider the table, sales, which contains data for the current month in addition to the previous 12 months. On January 1, 1999, you add a partition for January, which is stored in tablespace tsx.

ALTER TABLE sales

      ADD PARTITION jan99 VALUES LESS THAN ( '01-FEB-1999' )

      TABLESPACE tsx;

Local and global indexes associated with the range-partitioned table remain usable.

Adding a Partition to a Hash-Partitioned Table

When you add a partition to a hash-partitioned table, the database populates the new partition with rows rehashed from an existing partition (selected by the database) as determined by the hash function. As a result, if the table contains data, then it may take some time to add a hash partition.

The following statements show two ways of adding a hash partition to table scubagear. Choosing the first statement adds a new hash partition whose partition name is system generated, and which is placed in the default tablespace. The second statement also adds a new hash partition, but that partition is explicitly named p_named and is created in tablespace gear5.

ALTER TABLE scubagear ADD PARTITION;


ALTER TABLE scubagear

      ADD PARTITION p_named TABLESPACE gear5;

Indexes may be marked UNUSABLE as explained in the following table:

Table Type Index Behavior
Regular (Heap) Unless you specify UPDATE INDEXES as part of the ALTER TABLE statement:
  • The local indexes for the new partition, and for the existing partition from which rows were redistributed, are marked UNUSABLE and must be rebuilt.

  • All global indexes, or all partitions of partitioned global indexes, are marked UNUSABLE and must be rebuilt.

Index-organized
  • For local indexes, the behavior is the same as for heap tables.
  • All global indexes remain usable.


Adding a Partition to a List-Partitioned Table

The following statement illustrates how to add a new partition to a list-partitioned table. In this example physical attributes and NOLOGGING are specified for the partition being added.

ALTER TABLE q1_sales_by_region 

   ADD PARTITION q1_nonmainland VALUES ('HI', 'PR')

      STORAGE (INITIAL 20K NEXT 20K) TABLESPACE tbs_3

      NOLOGGING;

Any value in the set of literal values that describe the partition being added must not exist in any of the other partitions of the table.

You cannot add a partition to a list-partitioned table that has a default partition, but you can split the default partition. By doing so, you effectively create a new partition defined by the values that you specify, and a second partition that remains the default partition.

Local and global indexes associated with the list-partitioned table remain usable.

Adding a Partition to an Interval-Partitioned Table

You cannot explicitly add a partition to an interval-partitioned table unless you first lock the partition, which triggers the creation of the partition. The database automatically creates a partition for an interval when data for that interval is inserted. In general, you only need to explicitly create interval partitions for a partition exchange load scenario.

To change the interval for future partitions, use the SET INTERVAL clause of the ALTER TABLE statement. This clause changes the interval for partitions beyond the current highest boundary of all materialized interval partitions.

You also use the SET INTERVAL clause to migrate an existing range partitioned or range-* composite partitioned table into an interval or interval-* partitioned table. If you want to disable the creation of future interval partitions, and effectively revert back to a range-partitioned table, then use an empty value in the SET INTERVAL clause. Created interval partitions will then be transformed into range partitions with their current high values.

To increase the interval for date ranges, then you need to ensure that you are at a relevant boundary for the new interval. For example, if the highest interval partition boundary in your daily interval partitioned table transactions is January 30, 2007 and you want to change to a monthly partition interval, then the following statement results in an error:

ALTER TABLE transactions SET INTERVAL (NUMTOYMINTERVAL(1,'MONTH');


ORA-14767: Cannot specify this interval with existing high bounds

You need to create another daily partition with a high bound of February 1, 2007 in order to successfully change to a monthly interval:

LOCK TABLE transactions PARTITION FOR(TO_DATE('31-JAN-2007','dd-MON-yyyy') IN SHARE MODE;


ALTER TABLE transactions SET INTERVAL (NUMTOYMINTERVAL(1,'MONTH');

The lower partitions of an interval-partitioned table are range partitions. You can split range partitions in order to add more partitions in the range portion of the interval-partitioned table.

In order to disable interval partitioning on the transactions table, use:

ALTER TABLE transactions SET INTERVAL ();

Adding Partitions to a Composite [Range | List | Interval]-Hash Partitioned Table

Partitions can be added at both the partition level and at the hash subpartition level.

Adding a Partition to a [Range | List | Interval]-Hash Partitioned Table

Adding a new partition to a [range | list | interval]-hash partitioned table is as described previously. For an interval-hash partitioned table, interval partitions are automatically created. You can specify a SUBPARTITIONS clause that lets you add a specified number of subpartitions, or a SUBPARTITION clause for naming specific subpartitions. If no SUBPARTITIONS or SUBPARTITION clause is specified, then the partition inherits table level defaults for subpartitions. For an interval-hash partitioned table, you can only add subpartitions to range or interval partitions that have been materialized.

This example adds a range partition q1_2000 to the range-hash partitioned table sales, which will be populated with data for the first quarter of the year 2000. There are eight subpartitions stored in tablespace tbs5. The subpartitions cannot be set explicitly to use table compression. Subpartitions inherit the compression attribute from the partition level and are stored in a compressed form in this example:

ALTER TABLE sales ADD PARTITION q1_2000

      VALUES LESS THAN (2000, 04, 01) COMPRESS

      SUBPARTITIONS 8 STORE IN tbs5;
Adding a Subpartition to a [Range | List | Interval]-Hash Partitioned Table

You use the MODIFY PARTITION ... ADD SUBPARTITION clause of the ALTER TABLE statement to add a hash subpartition to a [range | list | interval]-hash partitioned table. The newly added subpartition is populated with rows rehashed from other subpartitions of the same partition as determined by the hash function. For an interval-hash partitioned table, you can only add subpartitions to range or interval partitions that have been materialized.

In the following example, a new hash subpartition us_loc5, stored in tablespace us1, is added to range partition locations_us in table diving.

ALTER TABLE diving MODIFY PARTITION locations_us

      ADD SUBPARTITION us_locs5 TABLESPACE us1;

Index subpartitions corresponding to the added and rehashed subpartitions must be rebuilt unless you specify UPDATE INDEXES.

Adding Partitions to a Composite [Range | List | Interval]-List Partitioned Table

Partitions can be added at both the partition level and at the list subpartition level.

Adding a Partition to a [Range | List | Interval]-List Partitioned Table

Adding a new partition to a [range | list | interval]-list partitioned table is as described previously. The database automatically creates interval partitions as data for a specific interval is inserted. You can specify SUBPARTITION clauses for naming and providing value lists for the subpartitions. If no SUBPARTITION clauses are specified, then the partition inherits the subpartition template. If there is no subpartition template, then a single default subpartition is created.

The following statement adds a new partition to the quarterly_regional_sales table that is partitioned by the range-list method. Some new physical attributes are specified for this new partition while table-level defaults are inherited for those that are not specified.

ALTER TABLE quarterly_regional_sales 

   ADD PARTITION q1_2000 VALUES LESS THAN (TO_DATE('1-APR-2000','DD-MON-YYYY'))

      STORAGE (INITIAL 20K NEXT 20K) TABLESPACE ts3 NOLOGGING

         (

          SUBPARTITION q1_2000_northwest VALUES ('OR', 'WA'),

          SUBPARTITION q1_2000_southwest VALUES ('AZ', 'UT', 'NM'),

          SUBPARTITION q1_2000_northeast VALUES ('NY', 'VM', 'NJ'),

          SUBPARTITION q1_2000_southeast VALUES ('FL', 'GA'),

          SUBPARTITION q1_2000_northcentral VALUES ('SD', 'WI'),

          SUBPARTITION q1_2000_southcentral VALUES ('OK', 'TX')

         );
Adding a Subpartition to a [Range | List | Interval]-List Partitioned Table

You use the MODIFY PARTITION ... ADD SUBPARTITION clause of the ALTER TABLE statement to add a list subpartition to a [range | list | interval]-list partitioned table. For an interval-list partitioned table, you can only add subpartitions to range or interval partitions that have been materialized.

The following statement adds a new subpartition to the existing set of subpartitions in the range-list partitioned table quarterly_regional_sales. The new subpartition is created in tablespace ts2.

ALTER TABLE quarterly_regional_sales

   MODIFY PARTITION q1_1999 

      ADD SUBPARTITION q1_1999_south

         VALUES ('AR','MS','AL') tablespace ts2;

Adding Partitions to a Composite [Range | List | Interval]-Range Partitioned Table

Partitions can be added at both the partition level and at the range subpartition level.

Adding a Partition to a [Range | List | Interval]-Range Partitioned Table

Adding a new partition to a [range | list | interval]-range partitioned table is as described previously. The database automatically creates interval partitions for an interval-range partitioned table when data is inserted in a specific interval. You can specify a SUBPARTITION clause for naming and providing ranges for specific subpartitions. If no SUBPARTITION clause is specified, then the partition inherits the subpartition template specified at the table level. If there is no subpartition template, then a single subpartition with a maximum value of MAXVALUE is created.

This example adds a range partition p_2007_jan to the range-range partitioned table shipments, which will be populated with data for the shipments ordered in January 2007. There are three subpartitions. Subpartitions inherit the compression attribute from the partition level and are stored in a compressed form in this example:

ALTER TABLE shipments

   ADD PARTITION p_2007_jan

      VALUES LESS THAN (TO_DATE('01-FEB-2007','dd-MON-yyyy')) COMPRESS

      ( SUBPARTITION p07_jan_e VALUES LESS THAN (TO_DATE('15-FEB-2007','dd-MON-yyyy'))

      , SUBPARTITION p07_jan_a VALUES LESS THAN (TO_DATE('01-MAR-2007','dd-MON-yyyy'))

      , SUBPARTITION p07_jan_l VALUES LESS THAN (TO_DATE('01-APR-2007','dd-MON-yyyy'))

      ) ;

Adding a Subpartition to a [Range | List | Interval]-Range Partitioned Table

You use the MODIFY PARTITION ... ADD SUBPARTITION clause of the ALTER TABLE statement to add a range subpartition to a [range | list | interval]-range partitioned table. For an interval-range partitioned table, you can only add partitions to range or interval partitions that have already been materialized.

The following example adds a range subpartition to the shipments table that will contain all values with an order_date in January 2007 and a delivery_date on or after April 1, 2007.

ALTER TABLE shipments

   MODIFY PARTITION p_2007_jan

      ADD SUBPARTITION p07_jan_vl VALUES LESS THAN (MAXVALUE) ;

Adding a Partition or Subpartition to a Reference-Partitioned Table

A partition or subpartition can be added to a parent table in a reference partition definition just as partitions and subpartitions can be added to a range, hash, list, or composite partitioned table. The add operation will automatically cascade to any descendant reference partitioned tables. The DEPENDENT TABLES clause can be used to set specific properties for dependent tables when you add partitions or subpartitions to a master table.

Adding Index Partitions

You cannot explicitly add a partition to a local index. Instead, a new partition is added to a local index only when you add a partition to the underlying table. Specifically, when there is a local index defined on a table and you issue the ALTER TABLE statement to add a partition, a matching partition is also added to the local index. The database assigns names and default physical storage attributes to the new index partitions, but you can rename or alter them after the ADD PARTITION operation is complete.

You can effectively specify a new tablespace for an index partition in an ADD PARTITION operation by first modifying the default attributes for the index. For example, assume that a local index, q1_sales_by_region_locix, was created for list partitioned table q1_sales_by_region. If before adding the new partition q1_nonmainland, as shown in "Adding a Partition to a List-Partitioned Table", you had issued the following statement, then the corresponding index partition would be created in tablespace tbs_4.

ALTER INDEX q1_sales_by_region_locix

   MODIFY DEFAULT ATTRIBUTES TABLESPACE tbs_4;

Otherwise, it would be necessary for you to use the following statement to move the index partition to tbs_4 after adding it:

ALTER INDEX q1_sales_by_region_locix 

   REBUILD PARTITION q1_nonmainland TABLESPACE tbs_4;

 

You can add a partition to a hash-partitioned global index using the ADD PARTITION syntax of ALTER INDEX. The database adds hash partitions and populates them with index entries rehashed from an existing hash partition of the index, as determined by the hash function. The following statement adds a partition to the index hgidx shown in "Creating a Hash-Partitioned Global Index":

ALTER INDEX hgidx ADD PARTITION p5;

You cannot add a partition to a range-partitioned global index, because the highest partition always has a partition bound of MAXVALUE. If you want to add a new highest partition, use the ALTER INDEX ... SPLIT PARTITION statement.

Coalescing Partitions

Coalescing partitions is a way of reducing the number of partitions in a hash-partitioned table or index, or the number of subpartitions in a *-hash partitioned table. When a hash partition is coalesced, its contents are redistributed into one or more remaining partitions determined by the hash function. The specific partition that is coalesced is selected by the database, and is dropped after its contents have been redistributed. If you coalesce a hash partition or subpartition in the parent table of a reference-partitioned table definition, then the reference-partitioned table automatically inherits the new partitioning definition.

Index partitions may be marked UNUSABLE as explained in the following table:

Table Type Index Behavior
Regular (Heap) Unless you specify UPDATE INDEXES as part of the ALTER TABLE statement:
  • Any local index partition corresponding to the selected partition is also dropped. Local index partitions corresponding to the one or more absorbing partitions are marked UNUSABLE and must be rebuilt.

  • All global indexes, or all partitions of partitioned global indexes, are marked UNUSABLE and must be rebuilt.

Index-organized
  • Some local indexes are marked UNUSABLE as noted for heap indexes.
  • All global indexes remain usable.


Coalescing a Partition in a Hash-Partitioned Table

The ALTER TABLE ... COALESCE PARTITION statement is used to coalesce a partition in a hash-partitioned table. The following statement reduces by one the number of partitions in a table by coalescing a partition.

ALTER TABLE ouu1

     COALESCE PARTITION;

Coalescing a Subpartition in a *-Hash Partitioned Table

The following statement distributes the contents of a subpartition of partition us_locations into one or more remaining subpartitions (determined by the hash function) of the same partition. Note that for an interval-partitioned table, you can only coalesce hash subpartitions of materialized range or interval partitions. Basically, this operation is the inverse of the MODIFY PARTITION ... ADD SUBPARTITION clause discussed in "Adding a Subpartition to a [Range | List | Interval]-Hash Partitioned Table".

ALTER TABLE diving MODIFY PARTITION us_locations

     COALESCE SUBPARTITION;

Coalescing Hash-partitioned Global Indexes

You can instruct the database to reduce by one the number of index partitions in a hash-partitioned global index using the COALESCE PARTITION clause of ALTER INDEX. The database selects the partition to coalesce based on the requirements of the hash partition. The following statement reduces by one the number of partitions in the hgidx index, created in "Creating a Hash-Partitioned Global Index":

ALTER INDEX hgidx COALESCE PARTITION;

Dropping Partitions

You can drop partitions from range, interval, list, or composite *-[range | list] partitioned tables. For interval partitioned tables, you can only drop range or interval partitions that have been materialized. For hash-partitioned tables, or hash subpartitions of composite *-hash partitioned tables, you must perform a coalesce operation instead.

You cannot drop a partition from a reference-partitioned table. Instead, a drop operation on a parent table will cascade to all descendant tables.

Dropping Table Partitions

Use one of the following statements to drop a table partition or subpartition:

  • ALTER TABLE ... DROP PARTITION to drop a table partition

  • ALTER TABLE ... DROP SUBPARTITION to drop a subpartition of a composite *-[range | list] partitioned table

If you want to preserve the data in the partition, then use the MERGE PARTITION statement instead of the DROP PARTITION statement.

If local indexes are defined for the table, then this statement also drops the matching partition or subpartitions from the local index. All global indexes, or all partitions of partitioned global indexes, are marked UNUSABLE unless either of the following is true:

  • You specify UPDATE INDEXES (Cannot be specified for index-organized tables. Use UPDATE GLOBAL INDEXES instead.)

  • The partition being dropped or its subpartitions are empty

    Note:

    • You cannot drop the only partition in a table. Instead, you must drop the table.

    • You cannot drop the highest range partition in the range-partitioned section of an interval-partitioned or interval-* composite partitioned table.

The following sections contain some scenarios for dropping table partitions.

Dropping a Partition from a Table that Contains Data and Global Indexes

If the partition contains data and one or more global indexes are defined on the table, then use one of the following methods to drop the table partition.

Method 1

Leave the global indexes in place during the ALTER TABLE ... DROP PARTITION statement. Afterward, you must rebuild any global indexes (whether partitioned or not) because the index (or index partitions) will have been marked UNUSABLE. The following statements provide an example of dropping partition dec98 from the sales table, then rebuilding its global non-partitioned index.

ALTER TABLE sales DROP PARTITION dec98;

ALTER INDEX sales_area_ix REBUILD;

If index sales_area_ix were a range-partitioned global index, then all partitions of the index would require rebuilding. Further, it is not possible to rebuild all partitions of an index in one statement. You must issue a separate REBUILD statement for each partition in the index. The following statements rebuild the index partitions jan99_ix, feb99_ix, mar99_ix, ..., dec99_ix.

ALTER INDEX sales_area_ix REBUILD PARTITION jan99_ix;

ALTER INDEX sales_area_ix REBUILD PARTITION feb99_ix;

ALTER INDEX sales_area_ix REBUILD PARTITION mar99_ix;

...

ALTER INDEX sales_area_ix REBUILD PARTITION dec99_ix;

This method is most appropriate for large tables where the partition being dropped contains a significant percentage of the total data in the table.

Method 2

Issue the DELETE statement to delete all rows from the partition before you issue the ALTER TABLE ... DROP PARTITION statement. The DELETE statement updates the global indexes.

For example, to drop the first partition, issue the following statements:

DELETE FROM sales partition (dec98);

ALTER TABLE sales DROP PARTITION dec98;

This method is most appropriate for small tables, or for large tables when the partition being dropped contains a small percentage of the total data in the table.

Method 3

Specify UPDATE INDEXES in the ALTER TABLE statement. Doing so causes the global index to be updated at the time the partition is dropped.

ALTER TABLE sales DROP PARTITION dec98

     UPDATE INDEXES;
Dropping a Partition Containing Data and Referential Integrity Constraints

If a partition contains data and the table has referential integrity constraints, choose either of the following methods to drop the table partition. This table has a local index only, so it is not necessary to rebuild any indexes.

Method 1

If there is no data referencing the data in the partition you want to drop, then you can disable the integrity constraints on the referencing tables, issue the ALTER TABLE ... DROP PARTITION statement, then re-enable the integrity constraints.

This method is most appropriate for large tables where the partition being dropped contains a significant percentage of the total data in the table. If there is still data referencing the data in the partition to be dropped, then make sure to remove all the referencing data in order to be able to re-enable the referential integrity constraints.

Method 2

If there is data in the referencing tables, then you can issue the DELETE statement to delete all rows from the partition before you issue the ALTER TABLE ... DROP PARTITION statement. The DELETE statement enforces referential integrity constraints, and also fires triggers and generates redo and undo logs. The delete can succeed if you created the constraints with the ON DELETE CASCADE option, deleting all rows from referencing tables as well.

DELETE FROM sales partition (dec94);

ALTER TABLE sales DROP PARTITION dec94;

This method is most appropriate for small tables or for large tables when the partition being dropped contains a small percentage of the total data in the table.

Dropping Interval Partitions

You can drop interval partitions in an interval-partitioned table. This operation will drop the data for the interval only and leave the interval definition in tact. If data is inserted in the interval just dropped, then the database will again create an interval partition.

You can also drop range partitions in an interval-partitioned table. The rules for dropping a range partition in an interval-partitioned table follow the rules for dropping a range partition in a range-partitioned table. If you drop a range partition in the middle of a set of range partitions, then the lower boundary for the next range partition shifts to the lower boundary of the range partition you just dropped. You cannot drop the highest range partition in the range-partitioned section of an interval-partitioned table.

The following example drops the September 2007 interval partition from the sales table. There are only local indexes so no indexes will be invalidated.

ALTER TABLE sales DROP PARTITION FOR(TO_DATE('01-SEP-2007','dd-MON-yyyy'));

Dropping Index Partitions

You cannot explicitly drop a partition of a local index. Instead, local index partitions are dropped only when you drop a partition from the underlying table.

If a global index partition is empty, then you can explicitly drop it by issuing the ALTER INDEX ... DROP PARTITION statement. But, if a global index partition contains data, then dropping the partition causes the next highest partition to be marked UNUSABLE. For example, you would like to drop the index partition P1, and P2 is the next highest partition. You must issue the following statements:

ALTER INDEX npr DROP PARTITION P1;

ALTER INDEX npr REBUILD PARTITION P2;

Note:

You cannot drop the highest partition in a global index.

Exchanging Partitions

You can convert a partition (or subpartition) into a non-partitioned table, and a non-partitioned table into a partition (or subpartition) of a partitioned table by exchanging their data segments. You can also convert a hash-partitioned table into a partition of a composite *-hash partitioned table, or convert the partition of a composite *-hash partitioned table into a hash-partitioned table. Similarly, you can convert a [range | list]-partitioned table into a partition of a composite *-[range | list] partitioned table, or convert a partition of the composite *-[range | list] partitioned table into a [range | list]-partitioned table.

Exchanging table partitions is most useful when you have an application using non-partitioned tables that you want to convert to partitions of a partitioned table. For example, in data warehousing environments, exchanging partitions facilitates high-speed data loading of new, incremental data into an already existing partitioned table. Generically, OLTP as well as data warehousing environments benefit from exchanging old data partitions out of a partitioned table. The data is purged from the partitioned table without actually being deleted and can be archived separately afterwards.

When you exchange partitions, logging attributes are preserved. You can optionally specify if local indexes are also to be exchanged (INCLUDING INDEXES clause), and if rows are to be validated for proper mapping (WITH VALIDATION clause).

Note:

When you specify WITHOUT VALIDATION for the exchange partition operation, this is normally a fast operation because it involves only data dictionary updates. However, if the table or partitioned table involved in the exchange operation has a primary key or unique constraint enabled, then the exchange operation will be performed as if WITH VALIDATION were specified in order to maintain the integrity of the constraints.

To avoid the overhead of this validation activity, issue the following statement for each constraint before doing the exchange partition operation:

ALTER TABLE table_name
     DISABLE CONSTRAINT constraint_name KEEP INDEX

Then, enable the constraints after the exchange.

If you specify WITHOUT VALIDATION, then you have to make sure that the data to be exchanged belongs in the partition you exchange.

Unless you specify UPDATE INDEXES, the database marks UNUSABLE the global indexes or all global index partitions on the table whose partition is being exchanged. Global indexes or global index partitions on the table being exchanged remain invalidated. (You cannot use UPDATE INDEXES for index-organized tables. Use UPDATE GLOBAL INDEXES instead.)

Exchanging a Range, Hash, or List Partition

To exchange a partition of a range, hash, or list-partitioned table with a non-partitioned table, or the reverse, use the ALTER TABLE ... EXCHANGE PARTITION statement. An example of converting a partition into a non-partitioned table follows. In this example, table stocks can be range, hash, or list partitioned.

ALTER TABLE stocks

    EXCHANGE PARTITION p3 WITH TABLE stock_table_3;

Exchanging a Partition of an Interval Partitioned Table

You can exchange interval partitions in an interval-partitioned table. However, you have to make sure the interval partition has been created before you can exchange the partition. You can let the database create the partition by locking the interval partition.

The following example shows a partition exchange for the interval_sales table, interval-partitioned using monthly partitions as of January 1, 2004. This example shows how to add data for June 2007 to the table using partition exchange load. Assume there are only local indexes on the interval_sales table, and equivalent indexes have been created on the interval_sales_june_2007 table.

LOCK TABLE interval_sales

PARTITION FOR (TO_DATE('01-JUN-2007','dd-MON-yyyy'))

IN SHARE MODE;


ALTER TABLE interval_sales

EXCHANGE PARTITION FOR (TO_DATE('01-JUN-2007','dd-MON-yyyy'))

WITH TABLE interval_sales_jun_2007

INCLUDING INDEXES;

Note the use of the FOR syntax to identify a partition that was system-generated. The partition name can be used by querying the *_TAB_PARTITIONS data dictionary view to find out the system-generated partition name.

Exchanging a Partition of a Reference Partitioned Table

You can exchange partitions in a reference-partitioned table, but you have to make sure that data you reference is available in the respective partition in the parent table.

The following example shows a partition exchange load scenario for the range-partitioned orders table, and the reference partitioned order_items table. Note that the data in the order_items_dec_2006 table only contains order item data for orders with an order_date in December 2006.

ALTER TABLE orders

EXCHANGE PARTITION p_2006_dec

WITH TABLE orders_dec_2006

UPDATE GLOBAL INDEXES;


ALTER TABLE order_items_dec_2006

ADD CONSTRAINT order_items_dec_2006_fk

FOREIGN KEY (order_id)

REFERENCES orders(order_id) ;


ALTER TABLE order_items

EXCHANGE PARTITION p_2006_dec

WITH TABLE order_items_dec_2006;

Note that you have to use the UPDATE GLOBAL INDEXES or UPDATE INDEXES on the exchange partition of the parent table in order for the primary key index to remain usable. Note also that you have to create or enable the foreign key constraint on the order_items_dec_2006 table in order for the partition exchange on the reference-partitioned table to succeed.

Exchanging a Partition of a Table with Virtual Columns

You can exchange partitions in the presence of virtual columns. In order for a partition exchange on a partitioned table with virtual columns to succeed, you have to create a table that matches the definition of all non-virtual columns in a single partition of the partitioned table. You do not need to include the virtual column definitions, unless constraints or indexes have been defined on the virtual column.

In this case, you have to include the virtual column definition in order to match the partitioned table's constraint and index definitions. This scenario also applies to virtual column-based partitioned tables.

Exchanging a Hash-Partitioned Table with a *-Hash Partition

In this example, you are exchanging a whole hash-partitioned table, with all of its partitions, with the partition of a *-hash partitioned table and all of its hash subpartitions. The following example illustrates this concept for a range-hash partitioned table.

First, create a hash-partitioned table:

CREATE TABLE t1 (i NUMBER, j NUMBER)

     PARTITION BY HASH(i)

       (PARTITION p1, PARTITION p2);

Populate the table, then create a range-hash partitioned table as shown:

CREATE TABLE t2 (i NUMBER, j NUMBER)

     PARTITION BY RANGE(j)

     SUBPARTITION BY HASH(i)

        (PARTITION p1 VALUES LESS THAN (10)

            SUBPARTITION t2_pls1

            SUBPARTITION t2_pls2,

         PARTITION p2 VALUES LESS THAN (20)

            SUBPARTITION t2_p2s1

            SUBPARTITION t2_p2s2));

It is important that the partitioning key in table t1 is the same as the subpartitioning key in table t2.

To migrate the data in t1 to t2, and validate the rows, use the following statement:

ALTER TABLE t2 EXCHANGE PARTITION p1 WITH TABLE t1

     WITH VALIDATION;

Exchanging a Subpartition of a *-Hash Partitioned Table

Use the ALTER TABLE ... EXCHANGE SUBPARTITION statement to convert a hash subpartition of a *-hash partitioned table into a non-partitioned table, or the reverse. The following example converts the subpartition q3_1999_s1 of table sales into the non-partitioned table q3_1999. Local index partitions are exchanged with corresponding indexes on q3_1999.

ALTER TABLE sales EXCHANGE SUBPARTITION q3_1999_s1

      WITH TABLE q3_1999 INCLUDING INDEXES;

Exchanging a List-Partitioned Table with a *-List Partition

The semantics of the ALTER TABLE ... EXCHANGE PARTITION statement are the same as described previously in "Exchanging a Hash-Partitioned Table with a *-Hash Partition". The example below shows an exchange partition scenario for a list-list partitioned table.

CREATE TABLE customers_apac

( id            NUMBER

, name          VARCHAR2(50)

, email         VARCHAR2(100)

, region        VARCHAR2(4)

, credit_rating VARCHAR2(1)

)

PARTITION BY LIST (credit_rating)

( PARTITION poor VALUES ('P')

, PARTITION mediocre VALUES ('C')

, PARTITION good VALUES ('G')

, PARTITION excellent VALUES ('E')

);

Populate the table with APAC customers. Then create a list-list partitioned table:

CREATE TABLE customers

( id            NUMBER

, name          VARCHAR2(50)

, email         VARCHAR2(100)

, region        VARCHAR2(4)

, credit_rating VARCHAR2(1)

)

PARTITION BY LIST (region)

SUBPARTITION BY LIST (credit_rating)

SUBPARTITION TEMPLATE

( SUBPARTITION poor VALUES ('P')

, SUBPARTITION mediocre VALUES ('C')

, SUBPARTITION good VALUES ('G')

, SUBPARTITION excellent VALUES ('E')

)

(PARTITION americas VALUES ('AMER')

, PARTITION emea VALUES ('EMEA')

, PARTITION apac VALUES ('APAC')

);

It is important that the partitioning key in the customers_apac table matches the subpartitioning key in the customers table.

Next, exchange the apac partition.

ALTER TABLE customers

EXCHANGE PARTITION apac

WITH TABLE customers_apac

WITH VALIDATION;

Exchanging a Subpartition of a *-List Partitioned Table

The semantics of the ALTER TABLE ... EXCHANGE SUBPARTITION are the same as described previously in "Exchanging a Subpartition of a *-Hash Partitioned Table".

Exchanging a Range-Partitioned Table with a *-Range Partition

The semantics of the ALTER TABLE ... EXCHANGE PARTITION statement are the same as described previously in "Exchanging a Hash-Partitioned Table with a *-Hash Partition". The example below shows the orders table, which is interval partitioned by order_date, and subpartitioned by range on order_total. The example shows how to exchange a single monthly interval with a range-partitioned table.

CREATE TABLE orders_mar_2007

( id          NUMBER

, cust_id     NUMBER

, order_date  DATE

, order_total NUMBER

)

PARTITION BY RANGE (order_total)

( PARTITION p_small VALUES LESS THAN (1000)

, PARTITION p_medium VALUES LESS THAN (10000)

, PARTITION p_large VALUES LESS THAN (100000)

, PARTITION p_extraordinary VALUES LESS THAN (MAXVALUE)

);

Populate the table with orders for March 2007. Then create an interval-range partitioned table:

CREATE TABLE orders

( id          NUMBER

, cust_id     NUMBER

, order_date  DATE

, order_total NUMBER

)

PARTITION BY RANGE (order_date) INTERVAL (NUMTOYMINTERVAL(1,'MONTH'))

  SUBPARTITION BY RANGE (order_total)

  SUBPARTITION TEMPLATE

  ( SUBPARTITION p_small VALUES LESS THAN (1000)

  , SUBPARTITION p_medium VALUES LESS THAN (10000)

  , SUBPARTITION p_large VALUES LESS THAN (100000)

  , SUBPARTITION p_extraordinary VALUES LESS THAN (MAXVALUE)

  )

(PARTITION p_before_2007 VALUES LESS THAN (TO_DATE('01-JAN-2007','dd-

MON-yyyy')));

It is important that the partitioning key in the orders_mar_2007 table matches the subpartitioning key in the orders table.

Next, exchange the partition. Note that since an interval partition is to be exchanged, the partition is first locked to ensure that the partition is created.

LOCK TABLE orders PARTITION FOR (TO_DATE('01-MAR-2007','dd-MON-yyyy')) 

IN SHARE MODE;


ALTER TABLE orders

EXCHANGE PARTITION

FOR (TO_DATE('01-MAR-2007','dd-MON-yyyy'))

WITH TABLE orders_mar_2007

WITH VALIDATION;

Exchanging a Subpartition of a *-Range Partitioned Table

The semantics of the ALTER TABLE ... EXCHANGE SUBPARTITION are the same as described previously in "Exchanging a Subpartition of a *-Hash Partitioned Table".

Merging Partitions

Use the ALTER TABLE ... MERGE PARTITION statement to merge the contents of two partitions into one partition. The two original partitions are dropped, as are any corresponding local indexes.

You cannot use this statement for a hash-partitioned table or for hash subpartitions of a composite *-hash partitioned table.

You cannot merge partitions for a reference-partitioned table. Instead, a merge operation on a parent table will cascade to all descendant tables. However, you can use the DEPENDENT TABLES clause to set specific properties for dependent tables when you issue the merge operation on the master table to merge partitions or subpartitions.

If the involved partitions or subpartitions contain data, then indexes may be marked UNUSABLE as explained in the following table:

Table Type Index Behavior
Regular (Heap) Unless you specify UPDATE INDEXES as part of the ALTER TABLE statement:
  • The database marks UNUSABLE all resulting corresponding local index partitions or subpartitions.

  • Global indexes, or all partitions of partitioned global indexes, are marked UNUSABLE and must be rebuilt.

Index-organized
  • The database marks UNUSABLE all resulting corresponding local index partitions.
  • All global indexes remain usable.


Merging Range Partitions

You are allowed to merge the contents of two adjacent range partitions into one partition. Nonadjacent range partitions cannot be merged. The resulting partition inherits the higher upper bound of the two merged partitions.

One reason for merging range partitions is to keep historical data online in larger partitions. For example, you can have daily partitions, with the oldest partition rolled up into weekly partitions, which can then be rolled up into monthly partitions, and so on.

The following scripts create an example of merging range partitions.

First, create a partitioned table and create local indexes.

-- Create a Table with four partitions each on its own tablespace

-- Partitioned by range on the data column.

--

CREATE TABLE four_seasons

( 

        one DATE,

        two VARCHAR2(60),

        three NUMBER

)

PARTITION  BY RANGE ( one ) 

(

PARTITION quarter_one 

   VALUES LESS THAN ( TO_DATE('01-apr-1998','dd-mon-yyyy'))

   TABLESPACE quarter_one,

PARTITION quarter_two 

   VALUES LESS THAN ( TO_DATE('01-jul-1998','dd-mon-yyyy'))

   TABLESPACE quarter_two,

PARTITION quarter_three

   VALUES LESS THAN ( TO_DATE('01-oct-1998','dd-mon-yyyy'))

   TABLESPACE quarter_three,

PARTITION quarter_four

   VALUES LESS THAN ( TO_DATE('01-jan-1999','dd-mon-yyyy'))

   TABLESPACE quarter_four

);

-- 

-- Create local PREFIXED index on Four_Seasons

-- Prefixed because the leftmost columns of the index match the

-- Partitioning key 

--

CREATE INDEX i_four_seasons_l ON four_seasons ( one,two ) 

LOCAL ( 

PARTITION i_quarter_one TABLESPACE i_quarter_one,

PARTITION i_quarter_two TABLESPACE i_quarter_two,

PARTITION i_quarter_three TABLESPACE i_quarter_three,

PARTITION i_quarter_four TABLESPACE i_quarter_four

);

Next, merge partitions.

--

-- Merge the first two partitions 

--

ALTER TABLE four_seasons 

MERGE PARTITIONS quarter_one, quarter_two INTO PARTITION quarter_two

UPDATE INDEXES;

If you omit the UPDATE INDEXES clause from the preceding statement, then you must rebuild the local index for the affected partition.

-- Rebuild index for quarter_two, which has been marked unusable 

-- because it has not had all of the data from Q1 added to it.

-- Rebuilding the index will correct this.

--

ALTER TABLE four_seasons MODIFY PARTITION 

quarter_two REBUILD UNUSABLE LOCAL INDEXES;

Merging Interval Partitions

The contents of two adjacent interval partitions can be merged into one partition. Nonadjacent interval partitions cannot be merged. The first interval partition can also be merged with the highest range partition. The resulting partition inherits the higher upper bound of the two merged partitions.

Merging interval partitions always results in the transition point being moved to the higher upper bound of the two merged partitions. This means that the range section of the interval-partitioned table will be extended to the upper bound of the two merged partitions. Any materialized interval partitions with boundaries lower than the newly merged partition will automatically be converted into range partitions, with their upper boundaries defined by the upper boundaries of their intervals.

For example, consider the following interval-partitioned table transactions:

CREATE TABLE transactions

( id               NUMBER

, transaction_date DATE

, value            NUMBER

)

PARTITION BY RANGE (transaction_date)

INTERVAL (NUMTODSINTERVAL(1,'DAY'))

( PARTITION p_before_2007 VALUES LESS THAN (TO_DATE('01-JAN-2007','dd-MON-yyyy')));

Insert data into the interval section of the table. This will create the interval partitions for these days. Note that January 15, 2007 and January 16, 2007 are stored in adjacent interval partitions.

INSERT INTO transactions VALUES (1,TO_DATE('15-JAN-2007','dd-MON-yyyy'),100);

INSERT INTO transactions VALUES (2,TO_DATE('16-JAN-2007','dd-MON-yyyy'),600); 

INSERT INTO transactions VALUES (3,TO_DATE('30-JAN-2007','dd-MON-yyyy'),200);

Next, merge the two adjacent interval partitions. The new partition will again have a system-generated name.

ALTER TABLE transactions

MERGE PARTITIONS FOR(TO_DATE('15-JAN-2007','dd-MON-yyyy'))

, FOR(TO_DATE('16-JAN-2007','dd-MON-yyyy'));

The transition point for the transactions table has now moved to January 17, 2007. The range section of the interval-partitioned table contains two range partitions: values less than January 1, 2007 and values less than January 17, 2007. Values greater than January 17, 2007 fall in the interval portion of the interval-partitioned table.

Merging List Partitions

When you merge list partitions, the partitions being merged can be any two partitions. They do not need to be adjacent, as for range partitions, because list partitioning does not assume any order for partitions. The resulting partition consists of all of the data from the original two partitions. If you merge a default list partition with any other partition, the resulting partition will be the default partition.

The following statement merges two partitions of a table partitioned using the list method into a partition that inherits all of its attributes from the table-level default attributes. MAXEXTENTS is specified in the statement.

ALTER TABLE q1_sales_by_region 

   MERGE PARTITIONS q1_northcentral, q1_southcentral 

   INTO PARTITION q1_central 

      STORAGE(MAXEXTENTS 20);

The value lists for the two original partitions were specified as:

PARTITION q1_northcentral VALUES ('SD','WI')

PARTITION q1_southcentral VALUES ('OK','TX')

The resulting sales_west partition value list comprises the set that represents the union of these two partition value lists, or specifically:

('SD','WI','OK','TX')

Merging *-Hash Partitions

When you merge *-hash partitions, the subpartitions are rehashed into the number of subpartitions specified by SUBPARTITIONS n or the SUBPARTITION clause. If neither is included, table-level defaults are used.

Note that the inheritance of properties is different when a *-hash partition is split (discussed in "Splitting a *-Hash Partition"), as opposed to when two *-hash partitions are merged. When a partition is split, the new partitions can inherit properties from the original partition because there is only one parent. However, when partitions are merged, properties must be inherited from the table level.

For interval-hash partitioned tables, you can only merge two adjacent interval partitions, or the highest range partition with the first interval partition. As described in "Merging Interval Partitions", the transition point will move when you merge intervals in an interval-hash partitioned table.

The following example merges two range-hash partitions:

ALTER TABLE all_seasons

   MERGE PARTITIONS quarter_1, quarter_2 INTO PARTITION quarter_2

   SUBPARTITIONS 8;

Merging *-List Partitions

Partitions can be merged at the partition level and subpartitions can be merged at the list subpartition level.

Merging Partitions in a *-List Partitioned Table

Merging partitions in a *-list partitioned table is as described previously in "Merging Range Partitions". However, when you merge two *-list partitions, the resulting new partition inherits the subpartition descriptions from the subpartition template, if one exists. If no subpartition template exists, then a single default subpartition is created for the new partition.

For interval-list partitioned tables, you can only merge two adjacent interval partitions, or the highest range partition with the first interval partition. As described in "Merging Interval Partitions", the transition point will move when you merge intervals in an interval-list partitioned table.

The following statement merges two partitions in the range-list partitioned stripe_regional_sales table. A subpartition template exists for the table.

ALTER TABLE stripe_regional_sales

   MERGE PARTITIONS q1_1999, q2_1999 INTO PARTITION q1_q2_1999

      STORAGE(MAXEXTENTS 20);

Some new physical attributes are specified for this new partition while table-level defaults are inherited for those that are not specified. The new resulting partition q1_q2_1999 inherits the high-value bound of the partition q2_1999 and the subpartition value-list descriptions from the subpartition template description of the table.

The data in the resulting partitions consists of data from both the partitions. However, there may be cases where the database returns an error. This can occur because data may map out of the new partition when both of the following conditions exist:

  • Some literal values of the merged subpartitions were not included in the subpartition template

  • The subpartition template does not contain a default partition definition.

This error condition can be eliminated by always specifying a default partition in the default subpartition template.

Merging Subpartitions in a *-List Partitioned Table

You can merge the contents of any two arbitrary list subpartitions belonging to the same partition. The resulting subpartition value-list descriptor includes all of the literal values in the value lists for the partitions being merged.

The following statement merges two subpartitions of a table partitioned using range-list method into a new subpartition located in tablespace ts4:

ALTER TABLE quarterly_regional_sales

   MERGE SUBPARTITIONS q1_1999_northwest, q1_1999_southwest

      INTO SUBPARTITION q1_1999_west

         TABLESPACE ts4;

The value lists for the original two partitions were:

  • Subpartition q1_1999_northwest was described as ('WA','OR')

  • Subpartition q1_1999_southwest was described as ('AZ','NM','UT')

The resulting subpartition value list comprises the set that represents the union of these two subpartition value lists:

  • Subpartition q1_1999_west has a value list described as ('WA','OR','AZ','NM','UT')

The tablespace in which the resulting subpartition is located and the subpartition attributes are determined by the partition-level default attributes, except for those specified explicitly. If any of the existing subpartition names are being reused, then the new subpartition inherits the subpartition attributes of the subpartition whose name is being reused.

Merging *-Range Partitions

Partitions can be merged at the partition level and subpartitions can be merged at the range subpartition level.

Merging Partitions in a *-Range Partitioned Table

Merging partitions in a *-range partitioned table is as described previously in "Merging Range Partitions". However, when you merge two *-range partitions, the resulting new partition inherits the subpartition descriptions from the subpartition template, if one exists. If no subpartition template exists, then a single subpartition with an upper boundary MAXVALUE is created for the new partition.

For interval-range partitioned tables, you can only merge two adjacent interval partitions, or the highest range partition with the first interval partition. As described in "Merging Interval Partitions", the transition point will move when you merge intervals in an interval-range partitioned table.

The following statement merges two partitions in the monthly interval-range partitioned orders table. A subpartition template exists for the table.

ALTER TABLE orders

MERGE PARTITIONS FOR(TO_DATE('01-MAR-2007','dd-MON-yyyy')), 

FOR(TO_DATE('01-APR-2007','dd-MON-yyyy'))

INTO PARTITION p_pre_may_2007;

If the March 2007 and April 2007 partitions were still in the interval section of the interval-range partitioned table, then the merge operation would move the transition point to May 1, 2007.

The subpartitions for partition p_pre_may_2007 inherit their properties from the subpartition template. The data in the resulting partitions consists of data from both the partitions. However, there may be cases where the database returns an error. This can occur because data may map out of the new partition when both of the following conditions are met:

  • Some range values of the merged subpartitions were not included in the subpartition template.

  • The subpartition template does not have a subpartition definition with a MAXVALUE upper boundary.

The error condition can be eliminated by always specifying a subpartition with an upper boundary of MAXVALUE in the subpartition template.

Modifying Default Attributes

You can modify the default attributes of a table, or for a partition of a composite partitioned table. When you modify default attributes, the new attributes affect only future partitions, or subpartitions, that are created. The default values can still be specifically overridden when creating a new partition or subpartition. You can modify the default attributes of a reference-partitioned table.

Modifying Default Attributes of a Table

You can modify the default attributes that will be inherited for range, hash, list, interval, or reference partitions using the MODIFY DEFAULT ATTRIBUTES clause of ALTER TABLE.

For hash-partitioned tables, only the TABLESPACE attribute can be modified.

Modifying Default Attributes of a Partition

To modify the default attributes inherited when creating subpartitions, use the ALTER TABLE ... MODIFY DEFAULT ATTRIBUTES FOR PARTITION. The following statement modifies the TABLESPACE in which future subpartitions of partition p1 in range-hash partitioned table emp will reside.

ALTER TABLE emp

     MODIFY DEFAULT ATTRIBUTES FOR PARTITION p1 TABLESPACE ts1;

Because all subpartitions of a range-hash partitioned table must share the same attributes, except TABLESPACE, it is the only attribute that can be changed.

You cannot modify default attributes of interval partitions that have not yet been created. If you want to change the way in which future subpartitions in an interval-partitioned table are created, then you have to modify the subpartition template.

Modifying Default Attributes of Index Partitions

In similar fashion to table partitions, you can alter the default attributes that will be inherited by partitions of a range-partitioned global index, or local index partitions of partitioned tables. For this you use the ALTER INDEX ... MODIFY DEFAULT ATTRIBUTES statement. Use the ALTER INDEX ... MODIFY DEFAULT ATTRIBUTES FOR PARTITION statement if you are altering default attributes to be inherited by subpartitions of a composite partitioned table.

Modifying Real Attributes of Partitions

It is possible to modify attributes of an existing partition of a table or index.

You cannot change the TABLESPACE attribute. Use ALTER TABLESPACE ... MOVE PARTITION/SUBPARTITION to move a partition or subpartition to a new tablespace.

Modifying Real Attributes for a Range or List Partition

Use the ALTER TABLE ... MODIFY PARTITION statement to modify existing attributes of a range partition or list partition. You can modify segment attributes (except TABLESPACE), or you can allocate and deallocate extents, mark local index partitions UNUSABLE, or rebuild local indexes that have been marked UNUSABLE.

If this is a range partition of a *-hash partitioned table, then note the following:

  • If you allocate or deallocate an extent, this action is performed for every subpartition of the specified partition.

  • Likewise, changing any other attributes results in corresponding changes to those attributes of all the subpartitions for that partition. The partition level default attributes are changed as well. To avoid changing attributes of existing subpartitions, use the FOR PARTITION clause of the MODIFY DEFAULT ATTRIBUTES statement.

The following are some examples of modifying the real attributes of a partition.

This example modifies the MAXEXTENTS storage attribute for the range partition sales_q1 of table sales:

ALTER TABLE sales MODIFY PARTITION sales_q1

     STORAGE (MAXEXTENTS 10); 

All of the local index subpartitions of partition ts1 in range-hash partitioned table scubagear are marked UNUSABLE in the following example:

ALTER TABLE scubagear MODIFY PARTITION ts1 UNUSABLE LOCAL INDEXES;

For an interval-partitioned table you can only modify real attributes of range partitions or interval partitions that have been created.

Modifying Real Attributes for a Hash Partition

You also use the ALTER TABLE ... MODIFY PARTITION statement to modify attributes of a hash partition. However, because the physical attributes of individual hash partitions must all be the same (except for TABLESPACE), you are restricted to:

  • Allocating a new extent

  • Deallocating an unused extent

  • Marking a local index subpartition UNUSABLE

  • Rebuilding local index subpartitions that are marked UNUSABLE

The following example rebuilds any unusable local index partitions associated with hash partition P1 of table dept:

ALTER TABLE dept MODIFY PARTITION p1

     REBUILD UNUSABLE LOCAL INDEXES;

Modifying Real Attributes of a Subpartition

With the MODIFY SUBPARTITION clause of ALTER TABLE you can perform the same actions as listed previously for partitions, but at the specific composite partitioned table subpartition level. For example:

ALTER TABLE emp MODIFY SUBPARTITION p3_s1

     REBUILD UNUSABLE LOCAL INDEXES;

Modifying Real Attributes of Index Partitions

The MODIFY PARTITION clause of ALTER INDEX lets you modify the real attributes of an index partition or its subpartitions. The rules are very similar to those for table partitions, but unlike the MODIFY PARTITION clause for ALTER INDEX, there is no subclause to rebuild an unusable index partition, but there is a subclause to coalesce an index partition or its subpartitions. In this context, coalesce means to merge index blocks where possible to free them for reuse.

You can also allocate or deallocate storage for a subpartition of a local index, or mark it UNUSABLE, using the MODIFY PARTITION clause.

Modifying List Partitions: Adding Values

List partitioning allows you the option of adding literal values from the defining value list.

Adding Values for a List Partition

Use the MODIFY PARTITION ... ADD VALUES clause of the ALTER TABLE statement to extend the value list of an existing partition. Literal values being added must not have been included in any other partition value list. The partition value list for any corresponding local index partition is correspondingly extended, and any global indexes, or global or local index partitions, remain usable.

The following statement adds a new set of state codes ('OK', 'KS') to an existing partition list.

ALTER TABLE sales_by_region

   MODIFY PARTITION region_south

      ADD VALUES ('OK', 'KS');

The existence of a default partition can have a performance impact when adding values to other partitions. This is because in order to add values to a list partition, the database must check that the values being added do not already exist in the default partition. If any of the values do exist in the default partition, then an error is raised.

Note:

The database executes a query to check for the existence of rows in the default partition that correspond to the literal values being added. Therefore, it is advisable to create a local prefixed index on the table. This speeds up the execution of the query and the overall operation.

You cannot add values to a default list partition.

Adding Values for a List Subpartition

This operation is essentially the same as described for "Modifying List Partitions: Adding Values", however, you use a MODIFY SUBPARTITION clause instead of the MODIFY PARTITION clause. For example, to extend the range of literal values in the value list for subpartition q1_1999_southeast, use the following statement:

ALTER TABLE quarterly_regional_sales

   MODIFY SUBPARTITION q1_1999_southeast

      ADD VALUES ('KS');

Literal values being added must not have been included in any other subpartition value list within the owning partition. However, they can be duplicates of literal values in the subpartition value lists of other partitions within the table.

For an interval-list composite partitioned table, you can only add values to subpartitions of range partitions or interval partitions that have been created. If you want to add values to subpartitions of interval partitions that have not yet been created, then you have to modify the subpartition template.

Modifying List Partitions: Dropping Values

List partitioning allows you the option of dropping literal values from the defining value list.

Dropping Values from a List Partition

Use the MODIFY PARTITION ... DROP VALUES clause of the ALTER TABLE statement to remove literal values from the value list of an existing partition. The statement is always executed with validation, meaning that it checks to see if any rows exist in the partition that corresponds to the set of values being dropped. If any such rows are found then the database returns an error message and the operation fails. When necessary, use a DELETE statement to delete corresponding rows from the table before attempting to drop values.

Note:

You cannot drop all literal values from the value list describing the partition. You must use the ALTER TABLE ... DROP PARTITION statement instead.

The partition value list for any corresponding local index partition reflects the new value list, and any global index, or global or local index partitions, remain usable.

The following statement drops a set of state codes ('OK' and 'KS') from an existing partition value list.

ALTER TABLE sales_by_region

   MODIFY PARTITION region_south

      DROP VALUES ('OK', 'KS');

Note:

The database executes a query to check for the existence of rows in the partition that correspond to the literal values being dropped. Therefore, it is advisable to create a local prefixed index on the table. This speeds up the execution of the query and the overall operation.

You cannot drop values from a default list partition.

Dropping Values from a List Subpartition

This operation is essentially the same as described for "Modifying List Partitions: Dropping Values", however, you use a MODIFY SUBPARTITION clause instead of the MODIFY PARTITION clause. For example, to remove a set of literal values in the value list for subpartition q1_1999_southeast, use the following statement:

ALTER TABLE quarterly_regional_sales

   MODIFY SUBPARTITION q1_1999_southeast

      DROP VALUES ('KS');

For an interval-list composite partitioned table, you can only drop values from subpartitions of range partitions or interval partitions that have been created. If you want to drop values from subpartitions of interval partitions that have not yet been created, then you have to modify the subpartition template.

Modifying a Subpartition Template

You can modify a subpartition template of a composite partitioned table by replacing it with a new subpartition template. Any subsequent operations that use the subpartition template (such as ADD PARTITION or MERGE PARTITIONS) will now use the new subpartition template. Existing subpartitions remain unchanged.

If you modify a subpartition template of an interval-* composite partitioned table, then interval partitions that have not yet been created will use the new subpartition template.

Use the ALTER TABLE ... SET SUBPARTITION TEMPLATE statement to specify a new subpartition template. For example:

ALTER TABLE emp_sub_template

   SET SUBPARTITION TEMPLATE

         (SUBPARTITION e TABLESPACE ts1,

          SUBPARTITION f TABLESPACE ts2,

          SUBPARTITION g TABLESPACE ts3,

          SUBPARTITION h TABLESPACE ts4

         );

You can drop a subpartition template by specifying an empty list:

ALTER TABLE emp_sub_template

   SET SUBPARTITION TEMPLATE ( );

Moving Partitions

Use the MOVE PARTITION clause of the ALTER TABLE statement to:

  • Re-cluster data and reduce fragmentation

  • Move a partition to another tablespace

  • Modify create-time attributes

  • Store the data in compressed format using table compression

Typically, you can change the physical storage attributes of a partition in a single step using an ALTER TABLE/INDEX ... MODIFY PARTITION statement. However, there are some physical attributes, such as TABLESPACE, that you cannot modify using MODIFY PARTITION. In these cases, use the MOVE PARTITION clause. Modifying some other attributes, such as table compression, affects only future storage, but not existing data.

Note:

ALTER TABLE...MOVE does not permit DML on the partition while the command is executing. If you want to move a partition and leave it available for DML, see "Redefining Partitions Online".

If the partition being moved contains any data, indexes may be marked UNUSABLE according to the following table:

Table Type Index Behavior
Regular (Heap) Unless you specify UPDATE INDEXES as part of the ALTER TABLE statement:
  • The matching partition in each local index is marked UNUSABLE. You must rebuild these index partitions after issuing MOVE PARTITION.

  • Any global indexes, or all partitions of partitioned global indexes, are marked UNUSABLE.

Index-organized Any local or global indexes defined for the partition being moved remain usable because they are primary-key based logical rowids. However, the guess information for these rowids becomes incorrect.

Moving Table Partitions

Use the MOVE PARTITION clause to move a partition. For example, to move the most active partition to a tablespace that resides on its own set of disks (in order to balance I/O), not log the action, and compress the data, issue the following statement:

ALTER TABLE parts MOVE PARTITION depot2

     TABLESPACE ts094 NOLOGGING COMPRESS;

This statement always drops the old partition segment and creates a new segment, even if you do not specify a new tablespace.

If you are moving a partition of a partitioned index-organized table, then you can specify the MAPPING TABLE clause as part of the MOVE PARTITION clause, and the mapping table partition will be moved to the new location along with the table partition.

For an interval or interval-* partitioned table, you can only move range partitions or interval partitions that have been created. A partition move operation does not move the transition point in an interval or interval-* partitioned table.

You can move a partition in a reference-partitioned table independent of the partition in the master table.

Moving Subpartitions

The following statement shows how to move data in a subpartition of a table. In this example, a PARALLEL clause has also been specified.

ALTER TABLE scuba_gear MOVE SUBPARTITION bcd_types 

     TABLESPACE tbs23 PARALLEL (DEGREE 2);

You can move a subpartition in a reference-partitioned table independent of the subpartition in the master table.

Moving Index Partitions

The ALTER TABLE ... MOVE PARTITION statement for regular tables, marks all partitions of a global index UNUSABLE. You can rebuild the entire index by rebuilding each partition individually using the ALTER INDEX ... REBUILD PARTITION statement. You can perform these rebuilds concurrently.

You can also simply drop the index and re-create it.

Redefining Partitions Online

Oracle Database provides a mechanism to move a partition or to make other changes to the partition's physical structure without significantly affecting the availability of the partition for DML. The mechanism is called online table redefinition.

For information on redefining a single partition of a table, see Oracle Database Administrator's Guide.

Rebuilding Index Partitions

Some reasons for rebuilding index partitions include:

  • To recover space and improve performance

  • To repair a damaged index partition caused by media failure

  • To rebuild a local index partition after loading the underlying table partition with SQL*Loader or an import utility

  • To rebuild index partitions that have been marked UNUSABLE

  • To enable key compression for B-tree indexes

The following sections discuss options for rebuilding index partitions and subpartitions.

Rebuilding Global Index Partitions

You can rebuild global index partitions in two ways:

  • Rebuild each partition by issuing the ALTER INDEX ... REBUILD PARTITION statement (you can run the rebuilds concurrently).

  • Drop the entire global index and re-create it. This method is more efficient because the table is scanned only once.

For most maintenance operations on partitioned tables with indexes, you can optionally avoid the need to rebuild the index by specifying UPDATE INDEXES on your DDL statement.

Rebuilding Local Index Partitions

Rebuild local indexes using either ALTER INDEX or ALTER TABLE as follows:

  • ALTER INDEX ... REBUILD PARTITION/SUBPARTITION

    This statement rebuilds an index partition or subpartition unconditionally.

  • ALTER TABLE ... MODIFY PARTITION/SUBPARTITION ... REBUILD UNUSABLE LOCAL INDEXES

    This statement finds all of the unusable indexes for the given table partition or subpartition and rebuilds them. It only rebuilds an index partition if it has been marked UNUSABLE.

Using ALTER INDEX to Rebuild a Partition

The ALTER INDEX ... REBUILD PARTITION statement rebuilds one partition of an index. It cannot be used for composite-partitioned tables. Only real physical segments can be rebuilt with this command. When you re-create the index, you can also choose to move the partition to a new tablespace or change attributes.

For composite-partitioned tables, use ALTER INDEX ... REBUILD SUBPARTITION to rebuild a subpartition of an index. You can move the subpartition to another tablespace or specify a parallel clause. The following statement rebuilds a subpartition of a local index on a table and moves the index subpartition is another tablespace.

ALTER INDEX scuba

   REBUILD SUBPARTITION bcd_types

   TABLESPACE tbs23 PARALLEL (DEGREE 2);
Using ALTER TABLE to Rebuild an Index Partition

The REBUILD UNUSABLE LOCAL INDEXES clause of ALTER TABLE ... MODIFY PARTITION does not allow you to specify any new attributes for the rebuilt index partition. The following example finds and rebuilds any unusable local index partitions for table scubagear, partition p1.

ALTER TABLE scubagear

   MODIFY PARTITION p1 REBUILD UNUSABLE LOCAL INDEXES;

There is a corresponding ALTER TABLE ... MODIFY SUBPARTITION clause for rebuilding unusable local index subpartitions.

Renaming Partitions

It is possible to rename partitions and subpartitions of both tables and indexes. One reason for renaming a partition might be to assign a meaningful name, as opposed to a default system name that was assigned to the partition in another maintenance operation.

All partitioning methods support the FOR(value) method to identify a partition. You can use this method to rename a system-generated partition name into a more meaningful name. This is particularly useful in interval or interval-* partitioned tables.

You can independently rename partitions and subpartitions for reference-partitioned master and child tables. The rename operation on the master table is not cascaded to descendant tables.

Renaming a Table Partition

Rename a range, hash, or list partition, using the ALTER TABLE ... RENAME PARTITION statement. For example:

ALTER TABLE scubagear RENAME PARTITION sys_p636 TO tanks;

Renaming a Table Subpartition

Likewise, you can assign new names to subpartitions of a table. In this case you would use the ALTER TABLE ... RENAME SUBPARTITION syntax.

Renaming Index Partitions

Index partitions and subpartitions can be renamed in similar fashion, but the ALTER INDEX syntax is used.

Renaming an Index Partition

Use the ALTER INDEX ... RENAME PARTITION statement to rename an index partition.

The ALTER INDEX statement does not support the use of FOR(value) to identify a partition. You have to use the original partition name in the rename operation.

Renaming an Index Subpartition

This next statement simply shows how to rename a subpartition that has a system generated name that was a consequence of adding a partition to an underlying table:

ALTER INDEX scuba RENAME SUBPARTITION sys_subp3254 TO bcd_types;

Splitting Partitions

The SPLIT PARTITION clause of the ALTER TABLE or ALTER INDEX statement is used to redistribute the contents of a partition into two new partitions. Consider doing this when a partition becomes too large and causes backup, recovery, or maintenance operations to take a long time to complete or it is felt that there is simply too much data in the partition. You can also use the SPLIT PARTITION clause to redistribute the I/O load.

This clause cannot be used for hash partitions or subpartitions.

If the partition you are splitting contains any data, then indexes may be marked UNUSABLE as explained in the following table:

Table Type Index Behavior
Regular (Heap) Unless you specify UPDATE INDEXES as part of the ALTER TABLE statement:
  • The database marks UNUSABLE the new partitions (there are two) in each local index.

  • Any global indexes, or all partitions of partitioned global indexes, are marked UNUSABLE and must be rebuilt.

Index-organized
  • The database marks UNUSABLE the new partitions (there are two) in each local index.
  • All global indexes remain usable.


You cannot split partitions or subpartitions in a reference-partitioned table. When you split partitions or subpartitions in the parent table then the split is cascaded to all descendant tables. However, you can use the DEPENDENT TABLES clause to set specific properties for dependent tables when you issue the SPLIT statement on the master table to split partitions or subpartitions.

Splitting a Partition of a Range-Partitioned Table

You split a range partition using the ALTER TABLE ... SPLIT PARTITION statement. You specify a value of the partitioning key column within the range of the partition at which to split the partition. The first of the resulting two new partitions includes all rows in the original partition whose partitioning key column values map lower that the specified value. The second partition contains all rows whose partitioning key column values map greater than or equal to the specified value.

You can optionally specify new attributes for the two partitions resulting from the split. If there are local indexes defined on the table, this statement also splits the matching partition in each local index.

In the following example fee_katy is a partition in the table vet_cats, which has a local index, jaf1. There is also a global index, vet on the table. vet contains two partitions, vet_parta, and vet_partb.

To split the partition fee_katy, and rebuild the index partitions, issue the following statements:

ALTER TABLE vet_cats SPLIT PARTITION 

      fee_katy at (100) INTO ( PARTITION

      fee_katy1, PARTITION fee_katy2);

ALTER INDEX JAF1 REBUILD PARTITION fee_katy1;

ALTER INDEX JAF1 REBUILD PARTITION fee_katy2;

ALTER INDEX VET REBUILD PARTITION vet_parta;

ALTER INDEX VET REBUILD PARTITION vet_partb;

Note:

If you do not specify new partition names, the database assigns names of the form SYS_Pn. You can examine the data dictionary to locate the names assigned to the new local index partitions. You may want to rename them. Any attributes you do not specify are inherited from the original partition.

Splitting a Partition of a List-Partitioned Table

You split a list partition by using the ALTER TABLE ... SPLIT PARTITION statement. The SPLIT PARTITION clause enables you to specify a list of literal values that define a partition into which rows with corresponding partitioning key values are inserted. The remaining rows of the original partition are inserted into a second partition whose value list contains the remaining values from the original partition.

You can optionally specify new attributes for the two partitions that result from the split.

The following statement splits the partition region_east into two partitions:

ALTER TABLE sales_by_region 

   SPLIT PARTITION region_east VALUES ('CT', 'MA', 'MD') 

   INTO 

    ( PARTITION region_east_1 

         TABLESPACE tbs2,

      PARTITION region_east_2

        STORAGE (NEXT 2M PCTINCREASE 25)) 

   PARALLEL 5;

The literal value list for the original region_east partition was specified as:

PARTITION region_east VALUES ('MA','NY','CT','NH','ME','MD','VA','PA','NJ')

The two new partitions are:

  • region_east_1 with a literal value list of ('CT','MA','MD')

  • region_east_2 inheriting the remaining literal value list of ('NY','NH','ME','VA','PA','NJ')

The individual partitions have new physical attributes specified at the partition level. The operation is executed with parallelism of degree 5.

You can split a default list partition just like you split any other list partition. This is also the only means of adding a partition to a list-partitioned table that contains a default partition. When you split the default partition, you create a new partition defined by the values that you specify, and a second partition that remains the default partition.

The following example splits the default partition of sales_by_region, thereby creating a new partition:

ALTER TABLE sales_by_region 

   SPLIT PARTITION region_unknown VALUES ('MT', 'WY', 'ID') 

   INTO 

    ( PARTITION region_wildwest,

      PARTITION region_unknown);

Splitting a Partition of an Interval-Partitioned Table

You split a range or a materialized interval partition using the ALTER TABLE ... SPLIT PARTITION statement in an interval-partitioned table. Splitting a range partition in the interval-partitioned table is the same as described in "Splitting a Partition of a Range-Partitioned Table".

To split a materialized interval partition, you specify a value of the partitioning key column within the interval partition at which to split the partition. The first of the resulting two new partitions includes all rows in the original partition whose partitioning key column values map lower than the specified value. The second partition contains all rows whose partitioning key column values map greater than or equal to the specified value. The split partition operation will move the transition point up to the higher boundary of the partition you just split, and all materialized interval partitions lower than the newly split partitions are implicitly converted into range partitions, with their upper boundaries defined by the upper boundaries of the intervals.

You can optionally specify new attributes for the two range partitions resulting from the split. If there are local indexes defined on the table, then this statement also splits the matching partition in each local index. You cannot split interval partitions that have not yet been created.

The following example shows splitting the May 2007 partition in the monthly interval partitioned table transactions.

ALTER TABLE transactions

SPLIT PARTITION FOR(TO_DATE('01-MAY-2007','dd-MON-yyyy'))

AT (TO_DATE('15-MAY-2007','dd-MON-yyyy'));

Splitting a *-Hash Partition

This is the opposite of merging *-hash partitions. When you split *-hash partitions, the new subpartitions are rehashed into either the number of subpartitions specified in a SUBPARTITIONS or SUBPARTITION clause. Or, if no such clause is included, the new partitions inherit the number of subpartitions (and tablespaces) from the partition being split.

Note that the inheritance of properties is different when a *-hash partition is split, versus when two *-hash partitions are merged. When a partition is split, the new partitions can inherit properties from the original partition because there is only one parent. However, when partitions are merged, properties must be inherited from table level defaults because there are two parents and the new partition cannot inherit from either at the expense of the other.

The following example splits a range-hash partition:

ALTER TABLE all_seasons SPLIT PARTITION quarter_1 

     AT (TO_DATE('16-dec-1997','dd-mon-yyyy'))

     INTO (PARTITION q1_1997_1 SUBPARTITIONS 4 STORE IN (ts1,ts3),

           PARTITION q1_1997­_2);

The rules for splitting an interval-hash partitioned table follow the rules for splitting an interval-partitioned table. As described in "Splitting a Partition of an Interval-Partitioned Table", the transition point will be changed to the higher boundary of the split partition.

Splitting Partitions in a *-List Partitioned Table

Partitions can be split at both the partition level and at the list subpartition level.

Splitting a *-List Partition

Splitting a partition of a *-list partitioned table is similar to what is described in "Splitting a Partition of a Range-Partitioned Table". No subpartition literal value list can be specified for either of the new partitions. The new partitions inherit the subpartition descriptions from the original partition being split.

The following example splits the q1_1999 partition of the quarterly_regional_sales table:

ALTER TABLE quarterly_regional_sales SPLIT PARTITION q1_1999

   AT (TO_DATE('15-Feb-1999','dd-mon-yyyy'))

   INTO ( PARTITION q1_1999_jan_feb

             TABLESPACE ts1,

          PARTITION q1_1999_feb_mar

             STORAGE (NEXT 2M PCTINCREASE 25) TABLESPACE ts2) 

   PARALLEL 5;

This operation splits the partition q1_1999 into two resulting partitions: q1_1999_jan_feb and q1_1999_feb_mar. Both partitions inherit their subpartition descriptions from the original partition. The individual partitions have new physical attributes, including tablespaces, specified at the partition level. These new attributes become the default attributes of the new partitions. This operation is run with parallelism of degree 5.

The ALTER TABLE ... SPLIT PARTITION statement provides no means of specifically naming subpartitions resulting from the split of a partition in a composite partitioned table. However, for those subpartitions in the parent partition with names of the form partition name_subpartition name, the database generates corresponding names in the newly created subpartitions using the new partition names. All other subpartitions are assigned system generated names of the form SYS_SUBPn. System generated names are also assigned for the subpartitions of any partition resulting from the split for which a name is not specified. Unnamed partitions are assigned a system generated partition name of the form SYS_Pn.

The following query displays the subpartition names resulting from the previous split partition operation on table quarterly_regional_sales. It also reflects the results of other operations performed on this table in preceding sections of this chapter since its creation in "Creating Composite Range-List Partitioned Tables".

SELECT PARTITION_NAME, SUBPARTITION_NAME, TABLESPACE_NAME

  FROM DBA_TAB_SUBPARTITIONS

  WHERE TABLE_NAME='QUARTERLY_REGIONAL_SALES'

  ORDER BY PARTITION_NAME;


PARTITION_NAME       SUBPARTITION_NAME              TABLESPACE_NAME

-------------------- ------------------------------ ---------------

Q1_1999_FEB_MAR      Q1_1999_FEB_MAR_WEST           TS2

Q1_1999_FEB_MAR      Q1_1999_FEB_MAR_NORTHEAST      TS2

Q1_1999_FEB_MAR      Q1_1999_FEB_MAR_SOUTHEAST      TS2

Q1_1999_FEB_MAR      Q1_1999_FEB_MAR_NORTHCENTRAL   TS2

Q1_1999_FEB_MAR      Q1_1999_FEB_MAR_SOUTHCENTRAL   TS2

Q1_1999_FEB_MAR      Q1_1999_FEB_MAR_SOUTH          TS2

Q1_1999_JAN_FEB      Q1_1999_JAN_FEB_WEST           TS1

Q1_1999_JAN_FEB      Q1_1999_JAN_FEB_NORTHEAST      TS1

Q1_1999_JAN_FEB      Q1_1999_JAN_FEB_SOUTHEAST      TS1

Q1_1999_JAN_FEB      Q1_1999_JAN_FEB_NORTHCENTRAL   TS1

Q1_1999_JAN_FEB      Q1_1999_JAN_FEB_SOUTHCENTRAL   TS1

Q1_1999_JAN_FEB      Q1_1999_JAN_FEB_SOUTH          TS1

Q1_2000              Q1_2000_NORTHWEST              TS3

Q1_2000              Q1_2000_SOUTHWEST              TS3

Q1_2000              Q1_2000_NORTHEAST              TS3

Q1_2000              Q1_2000_SOUTHEAST              TS3

Q1_2000              Q1_2000_NORTHCENTRAL           TS3

Q1_2000              Q1_2000_SOUTHCENTRAL           TS3

Q2_1999              Q2_1999_NORTHWEST              TS4

Q2_1999              Q2_1999_SOUTHWEST              TS4

Q2_1999              Q2_1999_NORTHEAST              TS4

Q2_1999              Q2_1999_SOUTHEAST              TS4

Q2_1999              Q2_1999_NORTHCENTRAL           TS4

Q2_1999              Q2_1999_SOUTHCENTRAL           TS4

Q3_1999              Q3_1999_NORTHWEST              TS4

Q3_1999              Q3_1999_SOUTHWEST              TS4

Q3_1999              Q3_1999_NORTHEAST              TS4

Q3_1999              Q3_1999_SOUTHEAST              TS4

Q3_1999              Q3_1999_NORTHCENTRAL           TS4

Q3_1999              Q3_1999_SOUTHCENTRAL           TS4

Q4_1999              Q4_1999_NORTHWEST              TS4

Q4_1999              Q4_1999_SOUTHWEST              TS4

Q4_1999              Q4_1999_NORTHEAST              TS4

Q4_1999              Q4_1999_SOUTHEAST              TS4

Q4_1999              Q4_1999_NORTHCENTRAL           TS4

Q4_1999              Q4_1999_SOUTHCENTRAL           TS4


36 rows selected.
Splitting a *-List Subpartition

Splitting a list subpartition of a *-list partitioned table is similar to what is described in "Splitting a Partition of a List-Partitioned Table", but the syntax is that of SUBPARTITION rather than PARTITION. For example, the following statement splits a subpartition of the quarterly_regional_sales table:

ALTER TABLE quarterly_regional_sales SPLIT SUBPARTITION q2_1999_southwest

   VALUES ('UT') INTO

      ( SUBPARTITION q2_1999_utah

           TABLESPACE ts2,

        SUBPARTITION q2_1999_southwest

           TABLESPACE ts3

      ) 

   PARALLEL;

This operation splits the subpartition q2_1999_southwest into two subpartitions:

  • q2_1999_utah with literal value list of ('UT')

  • q2_1999_southwest which inherits the remaining literal value list of ('AZ','NM')

The individual subpartitions have new physical attributes that are inherited from the subpartition being split.

You can only split subpartitions in an interval-list partitioned table for range partitions or materialized interval partitions. If you want to change subpartition values for future interval partitions, then you have to modify the subpartition template.

Splitting a *-Range Partition

Splitting a partition of a *-range partitioned table is similar to what is described in "Splitting a Partition of a Range-Partitioned Table". No subpartition range values can be specified for either of the new partitions. The new partitions inherit the subpartition descriptions from the original partition being split.

The following example splits the May 2007 interval partition of the interval-range partitioned orders table:

ALTER TABLE orders

SPLIT PARTITION FOR(TO_DATE('01-MAY-2007','dd-MON-yyyy'))

AT (TO_DATE('15-MAY-2007','dd-MON-yyyy'))

INTO (PARTITION p_fh_may07,PARTITION p_sh_may2007);

This operation splits the interval partition FOR('01-MAY-2007') into two resulting partitions: p_fh_may07 and p_sh_may_2007. Both partitions inherit their subpartition descriptions from the original partition. Any interval partitions before the June 2007 partition have been converted into range partitions, as described in "Merging Interval Partitions".

The ALTER TABLE ... SPLIT PARTITION statement provides no means of specifically naming subpartitions resulting from the split of a partition in a composite partitioned table. However, for those subpartitions in the parent partition with names of the form partition name_subpartition name, the database generates corresponding names in the newly created subpartitions using the new partition names. All other subpartitions are assigned system generated names of the form SYS_SUBPn. System generated names are also assigned for the subpartitions of any partition resulting from the split for which a name is not specified. Unnamed partitions are assigned a system generated partition name of the form SYS_Pn.

The following query displays the subpartition names and high values resulting from the previous split partition operation on table orders. It also reflects the results of other operations performed on this table in preceding sections of this chapter since its creation.

BREAK ON partition_name


SELECT partition_name, subpartition_name, high_value

FROM user_tab_subpartitions

WHERE table_name = 'ORCERS'

ORDER BY partition_name, subpartition_position;


PARTITION_NAME            SUBPARTITION_NAME              HIGH_VALUE

------------------------- ------------------------------ ---------------

P_BEFORE_2007             P_BEFORE_2007_P_SMALL          1000

                          P_BEFORE_2007_P_MEDIUM         10000

                          P_BEFORE_2007_P_LARGE          100000

                          P_BEFORE_2007_P_EXTRAORDINARY  MAXVALUE

P_FH_MAY07                SYS_SUBP2985                   1000

                          SYS_SUBP2986                   10000

                          SYS_SUBP2987                   100000

                          SYS_SUBP2988                   MAXVALUE

P_PRE_MAY_2007            P_PRE_MAY_2007_P_SMALL         1000

                          P_PRE_MAY_2007_P_MEDIUM        10000

                          P_PRE_MAY_2007_P_LARGE         100000

                          P_PRE_MAY_2007_P_EXTRAORDINARY MAXVALUE

P_SH_MAY2007              SYS_SUBP2989                   1000

                          SYS_SUBP2990                   10000

                          SYS_SUBP2991                   100000

                          SYS_SUBP2992                   MAXVALUE

Splitting a *-Range Subpartition

Splitting a range subpartition of a *-range partitioned table is similar to what is described in "Splitting a Partition of a Range-Partitioned Table", but the syntax is that of SUBPARTITION rather than PARTITION. For example, the following statement splits a subpartition of the orders table:

ALTER TABLE orders

SPLIT SUBPARTITION p_pre_may_2007_p_large AT (50000)

INTO (SUBPARTITION p_pre_may_2007_med_large TABLESPACE TS4

     , SUBPARTITION p_pre_may_2007_large_large TABLESPACE TS5

     );

This operation splits the subpartition p_pre_may_2007_p_large into two subpartitions:

  • p_pre_may_2007_med_large with values between 10000 and 50000

  • p_pre_may_2007_large_large with values between 50000 and 100000

The individual subpartitions have new physical attributes that are inherited from the subpartition being split.

You can only split subpartitions in an interval-range partitioned table for range partitions or materialized interval partitions. If you want to change subpartition boundaries for future interval partitions, then you have to modify the subpartition template.

Splitting Index Partitions

You cannot explicitly split a partition in a local index. A local index partition is split only when you split a partition in the underlying table. However, you can split a global index partition as is done in the following example:

ALTER INDEX quon1 SPLIT 

    PARTITION canada AT ( 100 ) INTO 

    PARTITION canada1 ..., PARTITION canada2 ...);

ALTER INDEX quon1 REBUILD PARTITION canada1;

ALTER INDEX quon1 REBUILD PARTITION canada2;

The index being split can contain index data, and the resulting partitions do not require rebuilding, unless the original partition was previously marked UNUSABLE.

Optimizing SPLIT PARTITION and SPLIT SUBPARTITION Operations

Oracle Database implements a SPLIT PARTITION operation by creating two new partitions and redistributing the rows from the partition being split into the two new partitions. This is an expensive operation because it is necessary to scan all the rows of the partition being split and then insert them one-by-one into the new partitions. Further if you do not use the UPDATE INDEXES clause, both local and global indexes also require rebuilding.

Sometimes after a split operation, one of the new partitions contains all of the rows from the partition being split, while the other partition contains no rows. This is often the case when splitting the first partition of a table. The database can detect such situations and can optimize the split operation. This optimization results in a fast split operation that behaves like an add partition operation.

Specifically, the database can optimize and speed up SPLIT PARTITION operations if all of the following conditions are met:

  • One of the two resulting partitions must be empty.

  • The non-empty resulting partition must have storage characteristics identical to those of the partition being split. Specifically:

    • If the partition being split is composite, then the storage characteristics of each subpartition in the new non-empty resulting partition must be identical to those of the subpartitions of the partition being split.

    • If the partition being split contains a LOB column, then the storage characteristics of each LOB (sub)partition in the new non-empty resulting partition must be identical to those of the LOB (sub)partitions of the partition being split.

    • If a partition of an index-organized table with overflow is being split, then the storage characteristics of each overflow (sub)partition in the new nonempty resulting partition must be identical to those of the overflow (sub)partitions of the partition being split.

    • If a partition of an index-organized table with mapping table is being split, then the storage characteristics of each mapping table (sub)partition in the new nonempty resulting partition must be identical to those of the mapping table (sub)partitions of the partition being split.

If these conditions are met after the split, then all global indexes remain usable, even if you did not specify the UPDATE INDEXES clause. Local index (sub)partitions associated with both resulting partitions remain usable if they were usable before the split. Local index (sub)partition(s) corresponding to the non-empty resulting partition will be identical to the local index (sub)partition(s) of the partition that was split.

The same optimization holds for SPLIT SUBPARTITION operations.

Truncating Partitions

Use the ALTER TABLE ... TRUNCATE PARTITION statement to remove all rows from a table partition. Truncating a partition is similar to dropping a partition, except that the partition is emptied of its data, but not physically dropped.

You cannot truncate an index partition. However, if local indexes are defined for the table, the ALTER TABLE ... TRUNCATE PARTITION statement truncates the matching partition in each local index. Unless you specify UPDATE INDEXES, any global indexes are marked UNUSABLE and must be rebuilt. (You cannot use UPDATE INDEXES for index-organized tables. Use UPDATE GLOBAL INDEXES instead.)

Truncating a Table Partition

Use the ALTER TABLE ... TRUNCATE PARTITION statement to remove all rows from a table partition, with or without reclaiming space. Truncating a partition in an interval-partitioned table does not move the transition point. You can truncate partitions and subpartitions in a reference-partitioned table.

Truncating Table Partitions Containing Data and Global Indexes

If the partition contains data and global indexes, use one of the following methods to truncate the table partition.

Method 1

Leave the global indexes in place during the ALTER TABLE ... TRUNCATE PARTITION statement. In this example, table sales has a global index sales_area_ix, which is rebuilt.

ALTER TABLE sales TRUNCATE PARTITION dec98;

ALTER INDEX sales_area_ix REBUILD;

This method is most appropriate for large tables where the partition being truncated contains a significant percentage of the total data in the table.

Method 2

Issue the DELETE statement to delete all rows from the partition before you issue the ALTER TABLE ... TRUNCATE PARTITION statement. The DELETE statement updates the global indexes, and also fires triggers and generates redo and undo logs.

For example, to truncate the first partition, issue the following statements:

DELETE FROM sales PARTITION (dec98);

ALTER TABLE sales TRUNCATE PARTITION dec98;

This method is most appropriate for small tables, or for large tables when the partition being truncated contains a small percentage of the total data in the table.

Method 3

Specify UPDATE INDEXES in the ALTER TABLE statement. This causes the global index to be truncated at the time the partition is truncated.

ALTER TABLE sales TRUNCATE PARTITION dec98

     UPDATE INDEXES;
Truncating a Partition Containing Data and Referential Integrity Constraints

If a partition contains data and has referential integrity constraints, then you cannot truncate the partition. If no other data is referencing any data in the partition you want to remove, then choose either of the following methods to truncate the table partition.

Method 1

Disable the integrity constraints, issue the ALTER TABLE ... TRUNCATE PARTITION statement, then re-enable the integrity constraints. This method is most appropriate for large tables where the partition being truncated contains a significant percentage of the total data in the table. If there is still referencing data in other tables, then you have to remove that data in order to be able to re-enable the integrity constraints.

Method 2

Issue the DELETE statement to delete all rows from the partition before you issue the ALTER TABLE ... TRUNCATE PARTITION statement. The DELETE statement enforces referential integrity constraints, and also fires triggers and generates redo and undo logs. Data in referencing tables will be deleted if the foreign key constraints were created with the ON DELETE CASCADE option.

Note:

You can substantially reduce the amount of logging by setting the NOLOGGING attribute (using ALTER TABLE ... TRUNCATE PARTITION ... NOLOGGING) for the partition before deleting all of its rows.
DELETE FROM sales partition (dec94);

ALTER TABLE sales TRUNCATE PARTITION dec94;

This method is most appropriate for small tables, or for large tables when the partition being truncated contains a small percentage of the total data in the table.

Truncating a Subpartition

You use the ALTER TABLE ... TRUNCATE SUBPARTITION statement to remove all rows from a subpartition of a composite partitioned table. Corresponding local index subpartitions are also truncated.

The following statement shows how to truncate data in a subpartition of a table. In this example, the space occupied by the deleted rows is made available for use by other schema objects in the tablespace.

ALTER TABLE diving

   TRUNCATE SUBPARTITION us_locations

      DROP STORAGE;

Dropping Partitioned Tables

Oracle Database processes a DROP TABLE statement for a partitioned table in the same way that it processes the statement for a non-partitioned table. One exception that was introduced in Oracle Database 10g Release 2 is when you use the PURGE keyword.

To avoid running into resource constraints, the DROP TABLE...PURGE statement for a partitioned table drops the table in multiple transactions, where each transaction drops a subset of the partitions or subpartitions and then commits. The table becomes completely dropped at the conclusion of the final transaction. This behavior comes with some changes to the DROP TABLE statement that you should be aware of.

First, if the DROP TABLE...PURGE statement fails, you can take corrective action, if any, and then reissue the statement. The statement resumes at the point where it failed.

Second, while the DROP TABLE...PURGE statement is in progress, the table is marked as unusable by setting the STATUS column to the value UNUSABLE in the following data dictionary views:

You can list all UNUSABLE partitioned tables by querying the STATUS column of these views.

Queries against other data dictionary views pertaining to partitioning, such as DBA_TAB_PARTITIONS and DBA_TAB_SUBPARTITIONS, exclude rows belonging to an UNUSABLE table. A complete list of these views is available in "Viewing Information About Partitioned Tables and Indexes".

After a table is marked UNUSABLE, the only statement that can be issued against it is another DROP TABLE...PURGE statement, and only if the previous DROP TABLE...PURGE statement failed. Any other statement issued against an UNUSABLE table results in an error. The table remains in the UNUSABLE state until the drop operation is complete.

See Also:

Partitioned Tables and Indexes Example

This section presents an example of moving the time window in a historical table.

A historical table describes the business transactions of an enterprise over intervals of time. Historical tables can be base tables, which contain base information; for example, sales, checks, and orders. Historical tables can also be rollup tables, which contain summary information derived from the base information using operations such as GROUP BY, AVERAGE, or COUNT.

The time interval in a historical table is often a rolling window. DBAs periodically delete sets of rows that describe the oldest transactions, and in turn allocate space for sets of rows that describe the most recent transactions. For example, at the close of business on April 30, 1995, the DBA deletes the rows (and supporting index entries) that describe transactions from April 1994, and allocates space for the April 1995 transactions.

Now consider a specific example. You have a table, order, which contains 13 months of transactions: a year of historical data in addition to orders for the current month. There is one partition for each month. These monthly partitions are named order_yymm, as are the tablespaces in which they reside.

The order table contains two local indexes, order_ix_onum, which is a local, prefixed, unique index on the order number, and order_ix_supp, which is a local, non-prefixed index on the supplier number. The local index partitions are named with suffixes that match the underlying table. There is also a global unique index, order_ix_cust, for the customer name. order_ix_cust contains three partitions, one for each third of the alphabet. So on October 31, 1994, change the time window on order as follows:

  1. Back up the data for the oldest time interval.

    ALTER TABLESPACE order_9310 BEGIN BACKUP;
    
    ...
    
    ALTER TABLESPACE order_9310 END BACKUP;
    
    
  2. Drop the partition for the oldest time interval.

    ALTER TABLE order DROP PARTITION order_9310;
    
    
  3. Add the partition to the most recent time interval.

    ALTER TABLE order ADD PARTITION order_9411;
    
    
  4. Re-create the global index partitions.

    ALTER INDEX order_ix_cust REBUILD PARTITION order_ix_cust_AH;
    
    ALTER INDEX order_ix_cust REBUILD PARTITION order_ix_cust_IP;
    
    ALTER INDEX order_ix_cust REBUILD PARTITION order_ix_cust_QZ;
    
    

Ordinarily, the database acquires sufficient locks to ensure that no operation (DML, DDL, or utility) interferes with an individual DDL statement, such as ALTER TABLE ... DROP PARTITION. However, if the partition maintenance operation requires several steps, it is the database administrator's responsibility to ensure that applications (or other maintenance operations) do not interfere with the multistep operation in progress. Some methods for doing this are:

Viewing Information About Partitioned Tables and Indexes

The following views display information specific to partitioned tables and indexes:

View Description
DBA_PART_TABLES

ALL_PART_TABLES

USER_PART_TABLES

DBA view displays partitioning information for all partitioned tables in the database. ALL view displays partitioning information for all partitioned tables accessible to the user. USER view is restricted to partitioning information for partitioned tables owned by the user.
DBA_TAB_PARTITIONS

ALL_TAB_PARTITIONS

USER_TAB_PARTITIONS

Display partition-level partitioning information, partition storage parameters, and partition statistics generated by the DBMS_STATS package or the ANALYZE statement.
DBA_TAB_SUBPARTITIONS

ALL_TAB_SUBPARTITIONS

USER_TAB_SUBPARTITIONS

Display subpartition-level partitioning information, subpartition storage parameters, and subpartition statistics generated by the DBMS_STATS package or the ANALYZE statement.
DBA_PART_KEY_COLUMNS

ALL_PART_KEY_COLUMNS

USER_PART_KEY_COLUMNS

Display the partitioning key columns for partitioned tables.
DBA_SUBPART_KEY_COLUMNS

ALL_SUBPART_KEY_COLUMNS

USER_SUBPART_KEY_COLUMNS

Display the subpartitioning key columns for composite-partitioned tables (and local indexes on composite-partitioned tables).
DBA_PART_COL_STATISTICS

ALL_PART_COL_STATISTICS

USER_PART_COL_STATISTICS

Display column statistics and histogram information for the partitions of tables.
DBA_SUBPART_COL_STATISTICS

ALL_SUBPART_COL_STATISTICS

USER_SUBPART_COL_STATISTICS

Display column statistics and histogram information for subpartitions of tables.
DBA_PART_HISTOGRAMS

ALL_PART_HISTOGRAMS

USER_PART_HISTOGRAMS

Display the histogram data (end-points for each histogram) for histograms on table partitions.
DBA_SUBPART_HISTOGRAMS

ALL_SUBPART_HISTOGRAMS

USER_SUBPART_HISTOGRAMS

Display the histogram data (end-points for each histogram) for histograms on table subpartitions.
DBA_PART_INDEXES

ALL_PART_INDEXES

USER_PART_INDEXES

Display partitioning information for partitioned indexes.
DBA_IND_PARTITIONS

ALL_IND_PARTITIONS

USER_IND_PARTITIONS

Display the following for index partitions: partition-level partitioning information, storage parameters for the partition, statistics collected by the DBMS_STATS package or the ANALYZE statement.
DBA_IND_SUBPARTITIONS

ALL_IND_SUBPARTITIONS

USER_IND_SUBPARTITIONS

Display the following information for index subpartitions: partition-level partitioning information, storage parameters for the partition, statistics collected by the DBMS_STATS package or the ANALYZE statement.
DBA_SUBPARTITION_TEMPLATES

ALL_SUBPARTITION_TEMPLATES

USER_SUBPARTITION_TEMPLATES

Display information about existing subpartition templates.

See Also: