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18 Very Large Databases (VLDB) → This chapter contains an overview of VLDB topics, with emphasis on partitioning as a key component … of the VLDB strategy. It covers the following topics: Introduction to Partitioning Overview of … Partitioned Indexes Partitioning to Improve Performance See Also: Oracle Database VLDB and Partitioning … Guide for more information
Introduction to Partitioning → Partitioning addresses key issues in supporting very large tables and indexes by letting you decompose them into smaller and more manageable pieces called partitions. SQL queries and DML statements do not need to be modified in order to access partitioned tables. However, after partitions are defined, DDL statements can access and manipulate individuals partitions rather than entire tables or indexes.
Partitioned Tables → Tables can be partitioned into up to 1024K-1 separate partitions. Any table can be partitioned except those tables containing columns with LONG or LONG RAW datatypes. You can, however, use tables containing columns with CLOB or BLOB datatypes. Note: To reduce disk use and memory use (specifically, the buffer cache), you can store tables and partitioned tables in a compressed format inside the database.
Global Nonpartitioned Indexes → Global nonpartitioned indexes behave just like a nonpartitioned index. They are commonly used in OLTP environments and offer efficient access to any individual record.
Partitioned Indexes on Composite Partitions → Here are a few points to remember when using partitioned indexes on composite partitions: Subpartitioned indexes are always local and stored with the table subpartition by default. Tablespaces can be specified at either index or index subpartition levels.
Overview of Partitioned Indexes → , use a local index. See Also: Oracle Database VLDB and Partitioning Guide and Oracle Database
Partitioning to Improve Performance → Partitioning can help you improve performance and manageability. Some topics to keep in mind when using partitioning for these reasons are: Partition Pruning Partition-wise Joins
Local Partitioned Indexes → partitioning is not on the left prefix of the index columns. See Also: Oracle Database VLDB and
Miscellaneous Information about Creating Indexes on Partitioned Tables → You can create bitmap indexes on partitioned tables, with the restriction that the bitmap indexes must be local to the partitioned table. They cannot be global indexes. Global indexes can be unique. Local indexes can only be unique if the partitioning key is a part of the index key.
Using Partitioned Indexes in Data Warehousing and DSS Applications → Here are a few guidelines for data warehousing and DSS applications: Local indexes are preferable because they are easier to manage during data loads and during partition-maintenance operations. Local indexes can improve performance because many index partitions can be scanned in parallel by range queries on the index key.
Partition Pruning → Oracle Database explicitly recognizes partitions and subpartitions. It then optimizes SQL statements to mark the partitions or subpartitions that need to be accessed and eliminates (prunes) unnecessary partitions or subpartitions from access by those SQL statements. In other words, partition pruning is the skipping of unnecessary index and data partitions or subpartitions in a query. For each SQL
Partitioning Methods → Oracle provides the following partitioning methods: Range partitioning maps data to partitions based on ranges of partition key values that you establish for each partition. Interval partitioning is an extension of range partitioning which instructs the database to automatically create partitions of a specified interval when data inserted into the table exceeds all of the range partitions. Hash partitioning
Global Partitioned Indexes → Oracle Database offers two types of global partitioned index: range partitioned and hash partitioned. This section includes the following topics: Global Range Partitioned Indexes Global Hash Partitioned Indexes Maintenance of Global Partitioned Indexes Global Range Partitioned Indexes Global range partitioned indexes are flexible in that the degree of partitioning and the partitioning key are independent
Using Partitioned Indexes in OLTP Applications → Here are a few guidelines for OLTP applications: Global indexes and unique, local indexes provide better performance than nonunique local indexes because they minimize the number of index partition probes. Local indexes offer better availability when there are partition or subpartition maintenance operations on the table. Hash-partitioned global indexes offer better performance by spreading out contention
Partition-wise Joins → joins by taking into account data distribution. See Also: Oracle Database VLDB and Partitioning Guide
Partition Key → Each row in a partitioned table is unambiguously assigned to a single partition. The partition key is a set of one or more columns that determines the partition for each row. Oracle Database automatically directs insert, update, and delete operations to the appropriate partition through the use of the partition key. A partition key: Consists of an ordered list of 1 to 16 columns Cannot contain a LEVEL,
Partitioned Index-Organized Tables → You can partition index-organized tables by range, list, or hash. Partitioned index-organized tables are very useful for providing improved manageability, availability, and performance for index-organized tables. In addition, data cartridges that use index-organized tables can take advantage of the ability to partition their stored data. For partitioning an index-organized table: Partition columns
Contents → Conventions 1 Introduction to Very Large Databases Introduction to Partitioning VLDB and Partitioning
VLDB and Partitioning → A very large database has no minimum absolute size. Although a VLDB is a database like smaller … databases, there are specific challenges in managing a VLDB. These challenges are related to the sheer … backup and recovery for a VLDB. Storage is a key component of a very large database. Chapter 9 focuses on best practices for storage