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Oracle® Database Performance Tuning Guide
12c Release 1 (12.1)

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15 Tuning the Result Cache

This chapter describes how to tune the result cache and contains the following topics:

15.1 About the Result Cache

A result cache is an area of memory, either in the Shared Global Area (SGA) or client application memory, that stores the results of a database query or query block for reuse. The cached rows are shared across SQL statements and sessions unless they become stale.

This section describes the two types of result cache and contains the following topics:

15.1.1 Server Result Cache Concepts

The server result cache is a memory pool within the shared pool. This memory pool consists of the SQL query result cache—which stores results of SQL queries—and the PL/SQL function result cache, which stores values returned by PL/SQL functions.

This section describes the server result cache and contains the following topics:

See Also:

15.1.1.1 Benefits of Using the Server Result Cache

The benefits of using the server result cache depend on the application. OLAP applications can benefit significantly from its use. Good candidates for caching are queries that access a high number of rows but return a small number, such as those in a data warehouse. For example, you can use advanced query rewrite with equivalences to create materialized views that materialize queries in the result cache instead of using tables.

See Also:

Oracle Database Data Warehousing Guide for information about using the result cache and advance query rewrite with equivalences

15.1.1.2 Understanding How the Server Result Cache Works

When a query executes, the database searches the cache memory to determine whether the result exists in the result cache. If the result exists, then the database retrieves the result from memory instead of executing the query. If the result is not cached, then the database executes the query, returns the result as output, and stores the result in the result cache.

When users execute queries and functions repeatedly, the database retrieves rows from the cache, decreasing response time. Cached results become invalid when data in dependent database objects is modified.

The following sections contains examples of how to retrieve results from the server result cache:

15.1.1.2.1 How Results are Retrieved in a Query

Example 15-1 shows a query of hr.employees that uses the RESULT_CACHE hint to retrieve rows from the server result cache.

Example 15-1 RESULT_CACHE Hint Specified in a Query

SELECT /*+ RESULT_CACHE */ department_id, AVG(salary)
  FROM hr.employees
 GROUP BY department_id;

A portion of the execution plan of this query might look like the following:

--------------------------------------------------------------
| Id | Operation          | Name                       |Rows
--------------------------------------------------------------
| 0 | SELECT STATEMENT    |                            | 11
| 1 |  RESULT CACHE       | 8fpza04gtwsfr6n595au15yj4y |
| 2 |   HASH GROUP BY     |                            | 11
| 3 |    TABLE ACCESS FULL| EMPLOYEES                  | 107
--------------------------------------------------------------

In this example, the results are retrieved directly from the cache, as indicated in step 1 of the execution plan. The value in the Name column is the cache ID of the result.

Example 15-2 shows a query of the V$RESULT_CACHE_OBJECTS view to retrieve detailed statistics about the cached result.

Example 15-2 Querying the V$RESULT_CACHE_OBJECTS View

SELECT id, type, creation_timestamp, block_count,
       column_count, pin_count, row_count
  FROM V$RESULT_CACHE_OBJECTS
 WHERE cache_id = '8fpza04gtwsfr6n595au15yj4y';

In this example, the value of CACHE_ID is the cache ID obtained from the explain plan in Example 15-1. The output of this query might look like the following:

        ID TYPE       CREATION_ BLOCK_COUNT COLUMN_COUNT  PIN_COUNT  ROW_COUNT
---------- ---------- --------- ----------- ------------ ---------- ----------
         2 Result     06-NOV-11           1            2          0         12
15.1.1.2.2 How Results are Retrieved in a View

Example 15-3 shows a query that uses the RESULT_CACHE hint within a WITH clause view.

Example 15-3 RESULT_CACHE Hint Specified in a WITH View

WITH summary AS
( SELECT /*+ RESULT_CACHE */ department_id, avg(salary) avg_sal
    FROM hr.employees
   GROUP BY department_id )
SELECT d.*, avg_sal
  FROM hr.departments d, summary s
 WHERE d.department_id = s.department_id;

A portion of the execution plan of this query might look like the following:

---------------------------------------------------------------------------------------------------
| Id  | Operation             | Name                       | Rows | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |                            |   11 |   517 |     7  (29)| 00:00:01 |
|*  1 |  HASH JOIN            |                            |   11 |   517 |     7  (29)| 00:00:01 |
|   2 |   VIEW                |                            |   11 |   286 |     4  (25)| 00:00:01 |
|   3 |    RESULT CACHE       | 8nknvkh64ctmz94a5muf2tyb8r |      |       |            |          |
|   4 |     HASH GROUP BY     |                            |   11 |    77 |     4  (25)| 00:00:01 |
|   5 |      TABLE ACCESS FULL| EMPLOYEES                  |  107 |   749 |     3   (0)| 00:00:01 |
|   6 |   TABLE ACCESS FULL   | DEPARTMENTS                |   27 |   567 |     2   (0)| 00:00:01 |
---------------------------------------------------------------------------------------------------

In this example, the summary view results are retrieved directly from the cache, as indicated in step 3 of the execution plan. The value in the Name column is the cache ID of the result.

15.1.2 Client Result Cache Concepts

The Oracle Call Interface (OCI) client result cache is a memory area inside a client process that caches SQL query result sets for OCI applications. This client cache exists for each client process and is shared by all sessions inside the process. Oracle recommends client result caching for queries of read-only or read-mostly tables.

Note:

The client result cache is distinct from the server result cache, which resides in the SGA. When client result caching is enabled, the query result set can be cached on the client, server, or both. Client caching can be enabled even if the server result cache is disabled.

This section describes the client result cache and contains the following topics:

15.1.2.1 Benefits of Using the Client Result Cache

OCI drivers, such as OCCI, the JDBC OCI driver, and ODP.NET, support client result caching. Performance benefits of using the client result cache include:

  • Reduced query response time

    When queries are executed repeatedly, the application retrieves results directly from the client cache memory, resulting in faster query response time.

  • More efficient use of database resources

    The reduction in server round trips may result in substantial performance savings of server resources, such as server CPU and I/O. These resources are freed for other tasks, thereby making the server more scalable.

  • Reduced memory cost

    The result cache uses client memory, which may be less expensive than server memory.

15.1.2.2 Understanding How the Client Result Cache Works

The client result cache stores the results of the outermost query, which are the columns defined by the OCI application. Subqueries and query blocks are not cached.

Figure 15-1 illustrates a client process with a database login session. This client process has one client result cache shared amongst multiple application sessions running in the client process. If the first application session runs a query, then it retrieves rows from the database and caches them in the client result cache. If other application sessions run the same query, then they also retrieve rows from the client result cache.

Figure 15-1 Client Result Cache

Description of Figure 15-1 follows
Description of "Figure 15-1 Client Result Cache"

The client result cache transparently keeps the result set consistent with session state or database changes that affect it. When a transaction changes the data or metadata of database objects used to build the cached result, the database sends an invalidation to the OCI client on its next round trip to the server.

See Also:

Oracle Call Interface Programmer's Guide for details about the client result cache

15.2 Configuring the Result Cache

This section describes how to configure the server and client result cache and contains the following topics:

15.2.1 Configuring the Server Result Cache

By default, on database startup, Oracle Database allocates memory to the server result cache in the shared pool. The memory size allocated depends on the memory size of the shared pool and the selected memory management system:

  • Automatic memory management

    If you are using the MEMORY_TARGET initialization parameter to specify memory allocation, Oracle Database allocates 0.25% of the value of the MEMORY_TARGET parameter to the result cache.

  • Automatic shared memory management

    If you are managing the size of the shared pool using the SGA_TARGET initialization parameter, Oracle Database allocates 0.50% of the value of the SGA_TARGET parameter to the result cache.

  • Manual shared memory management

    If you are managing the size of the shared pool using the SHARED_POOL_SIZE initialization parameter, then Oracle Database allocates 1% of the shared pool size to the result cache.

Note:

Oracle Database will not allocate more than 75% of the shared pool to the server result cache.

The size of the server result cache grows until it reaches the maximum size. Query results larger than the available space in the cache are not cached. The database employs a Least Recently Used (LRU) algorithm to age out cached results, but does not otherwise automatically release memory from the server result cache.

This section describes how to configure the server result cache and contains the following topics:

15.2.1.1 Sizing the Server Result Cache Using Initialization Parameters

Table 15-1 lists the database initialization parameters that control the server result cache.

Table 15-1 Server Result Cache Initialization Parameters

Parameter Description

RESULT_CACHE_MAX_SIZE

Specifies the memory allocated to the server result cache. To disable the server result cache, set this parameter to 0.

RESULT_CACHE_MAX_RESULT

Specifies the maximum amount of server result cache memory (in percent) that can be used for a single result. Valid values are between 1 and 100. The default value is 5%. You can set this parameter at the system or session level.

RESULT_CACHE_REMOTE_EXPIRATION

Specifies the expiration time (in minutes) for a result in the server result cache that depends on remote database objects. The default value is 0, which specifies that results using remote objects will not be cached. If a non-zero value is set for this parameter, DML on the remote database does not invalidate the server result cache.


To change the memory allocated to the server result cache: 

  • Set the value of the RESULT_CACHE_MAX_SIZE initialization parameter to the desired size.

    In an Oracle Real Application Clusters (Oracle RAC) environment, the result cache is specific to each database instance and can be sized differently on each instance. However, invalidations work across instances. To disable the server result cache in a cluster, you must explicitly set this parameter to 0 for each instance startup.

See Also:

Oracle Database Reference for information about the server result cache initialization parameters

15.2.1.2 Managing the Server Result Cache Using DBMS_RESULT_CACHE

The DBMS_RESULT_CACHE package provides statistics, information, and operators that enable you to manage memory allocation for the server result cache. Use the DBMS_RESULT_CACHE package to perform operations such as retrieving statistics on the cache memory usage and flushing the cache.

This section describes how to manage the server result cache using the DBMS_RESULT_CACHE package and contains the following topics:

15.2.1.2.1 Viewing Memory Usage Statistics for the Server Result Cache

This section describes how to view memory allocation statistics for the result cache using the DBMS_RESULT_CACHE package.

To view memory usage statistics for the result cache: 

  • Execute the DBMS_RESULT_CACHE.MEMORY_REPORT procedure.

    Example 15-4 shows an execution of this procedure.

Example 15-4 Using the DBMS_RESULT_CACHE Package

SQLSET SERVEROUTPUT ON
EXECUTE DBMS_RESULT_CACHE.MEMORY_REPORT

The output of this command might look like the following:

R e s u l t  C a c h e  M e m o r y  R e p o r t
[Parameters]
Block Size = 1024 bytes
Maximum Cache Size = 950272 bytes (928 blocks)
Maximum Result Size = 47104 bytes (46 blocks)
[Memory]
Total Memory = 46340 bytes [0.048% of the Shared Pool]
... Fixed Memory = 10696 bytes [0.011% of the Shared Pool]
... State Object Pool = 2852 bytes [0.003% of the Shared Pool]
... Cache Memory = 32792 bytes (32 blocks) [0.034% of the Shared Pool]
....... Unused Memory = 30 blocks
....... Used Memory = 2 blocks
........... Dependencies = 1 blocks
........... Results = 1 blocks
............... SQL = 1 blocks

PL/SQL procedure successfully completed.
15.2.1.2.2 Flushing the Server Result Cache

This section describes how to remove all existing results and purge the result cache memory using the DBMS_RESULT_CACHE package.

To flush the server result cache: 

  • Execute the DBMS_RESULT_CACHE.FLUSH procedure.

See Also:

Oracle Database PL/SQL Packages and Types Reference for information about the DBMS_RESULT_CACHE package

15.2.2 Configuring the Client Result Cache

Table 15-2 lists the database initialization parameters that enable or influence the behavior of the client result cache.

Table 15-2 Client Result Cache Initialization Parameters

Parameter Description

CLIENT_RESULT_CACHE_SIZE

Specifies the maximum size of the client result cache for each client process. To enable the client result cache, set the size to 32768 bytes or greater. A lesser value, including the default of 0, disables the client result cache.

Note: If the CLIENT_RESULT_CACHE_SIZE setting disables the client cache, then a client node cannot enable it. If the CLIENT_RESULT_CACHE_SIZE setting enables the client cache, however, then a client node can override the setting. For example, a client node can disable client result caching or increase the size of its cache.

CLIENT_RESULT_CACHE_LAG

Specifies the amount of lag time (in milliseconds) for the client result cache. The default value is 3000 (3 seconds). If the OCI application does not perform any database calls for a period of time, then this setting forces the next statement execution call to check for validations.

If the OCI application accesses the database infrequently, then setting this parameter to a low value results in more round trips from the OCI client to the database to keep the client result cache synchronized with the database.

COMPATIBLE

Specifies the release with which Oracle Database must maintain compatibility. For the client result cache to be enabled, this parameter must be set to 11.0.0.0 or higher. For client caching on views, this parameter must be set to 11.2.0.0.0 or higher.


An optional client configuration file overrides client result cache initialization parameters set in the server parameter file.

Note:

The client result cache lag can only be set with the CLIENT_RESULT_CACHE_LAG initialization parameter.

See Also:

15.2.3 Setting the Result Cache Mode

The result cache mode is a database setting that determines which queries are eligible to store result sets in the server and client result caches. If a query is eligible for caching, then the application checks the result cache to determine whether the query result set exists in the cache. If it exists, then the result is retrieved directly from the result cache. Otherwise, the database executes the query and returns the result as output and stores it in the result cache. Oracle recommends result caching for queries of read-only or read-mostly database objects.

When the result cache is enabled, the database also caches queries that call non-deterministic PL/SQL functions. When caching SELECT statements that call such functions, the result cache tracks data dependencies for the PL/SQL functions and the database objects. However, if the function uses data that are not being tracked (such as sequences, SYSDATE, SYS_CONTEXT, and package variables), using the result cache on queries that call this function can produce stale results. In this regard, the behavior of the result cache is identical to caching PL/SQL functions. Therefore, always consider data accuracy, as well as performance, when choosing to enable the result cache.

To set the result cache mode: 

  • Set the value of the RESULT_CACHE_MODE initialization parameter to determine the behavior of the result cache.

    You can set this parameter for the instance (ALTER SYSTEM), session (ALTER SESSION), or in the server parameter file.

    Table 15-3 describes the values for this parameter.

Table 15-3 Values for the RESULT_CACHE_MODE Parameter

Value Description

MANUAL

Query results can only be stored in the result cache by using a query hint or table annotation. This is the default and recommended value.

FORCE

All results are stored in the result cache. If a query result is not in the cache, then the database executes the query and stores the result in the cache. Subsequent executions of the same SQL statement, including the result cache hint, retrieve data from the cache. Sessions uses these results if possible. To exclude query results from the cache, the /*+ NO_RESULT_CACHE */ query hint must be used.

Note: FORCE mode is not recommended because the database and clients will attempt to cache all queries, which may create significant performance and latching overhead. Moreover, because queries that call non-deterministic PL/SQL functions are also cached, enabling the result cache in such a broad-based manner may cause material changes to the results.


See Also:

Oracle Database Reference for information about the RESULT_CACHE_MODE initialization parameter

15.2.4 Requirements for the Result Cache

Enabling the result cache does not guarantee that a specific result set will be included in the server or client result cache. In order for results to be cached, the following requirements must be met:

15.2.4.1 Read Consistency Requirements

For a snapshot to be reusable, it must have read consistency. For a result set to be eligible for caching, at least one of the following conditions must be true:

  • The read-consistent snapshot used to build the result must retrieve the most current, committed state of the data.

  • The query points to an explicit point in time using flashback query.

If the current session has an active transaction referencing objects in a query, then the results from this query are not eligible for caching.

15.2.4.2 Query Parameter Requirements

Cache results can be reused if they are parameterized with variable values when queries are equivalent and the parameter values are the same. Different values or bind variable names may cause cache misses. Results are parameterized if any of the following constructs are used in the query:

  • Bind variables

  • The SQL functions DBTIMEZONE, SESSIONTIMEZONE, USERENV/SYS_CONTEXT (with constant variables), UID, and USER

  • NLS parameters

15.2.4.3 Restrictions for the Result Cache

Results cannot be cached when the following objects or functions are in a query:

  • Temporary tables and tables in the SYS or SYSTEM schemas

  • Sequence CURRVAL and NEXTVAL pseudo columns

  • SQL functions CURRENT_DATE, CURRENT_TIMESTAMP, LOCAL_TIMESTAMP, USERENV/SYS_CONTEXT (with non-constant variables), SYS_GUID, SYSDATE, and SYS_TIMESTAMP

The client result cache has additional restrictions for result caching.

See Also:

Oracle Call Interface Programmer's Guide for information about additional restrictions for the client result cache

15.3 Specifying Queries for Result Caching

This section describes how to specify queries for result caching and contains the following topics:

15.3.1 Using SQL Result Cache Hints

Use result cache hints at the application level to control caching behavior. The SQL result cache hints take precedence over the result cache mode and result cache table annotations.

This section describes how to use SQL result cache hints and contains the following topics:

See Also:

Oracle Database SQL Language Reference for information about the RESULT_CACHE and NO_RESULT_CACHE hints

15.3.1.1 Using the RESULT_CACHE Hint

When the result cache mode is MANUAL, the /*+ RESULT_CACHE */ hint instructs the database to cache the results of a query block and to use the cached results in future executions.

Example 15-5 shows a query that uses the RESULT_CACHE hint.

Example 15-5 Using the RESULT_CACHE Hint

SELECT /*+ RESULT_CACHE */ prod_id, SUM(amount_sold)
  FROM sales 
 GROUP BY prod_id
 ORDER BY prod_id;

In this example, the query instructs the database to cache rows for a query of the sales table.

15.3.1.2 Using the NO_RESULT_CACHE Hint

The /*+ NO_RESULT_CACHE */ hint instructs the database not to cache the results in either the server or client result caches.

Example 15-6 shows a query that uses the NO_RESULT_CACHE hint.

Example 15-6 Using the NO_RESULT_CACHE Hint

SELECT /*+ NO_RESULT_CACHE */ prod_id, SUM(amount_sold) 
  FROM sales 
 GROUP BY prod_id
 ORDER BY prod_id;

In this example, the query instructs the database not to cache rows for a query of the sales table.

15.3.1.3 Using the RESULT_CACHE Hint in Views

The RESULT_CACHE hint applies only to the query block in which the hint is specified. If the hint is specified only in a view, then only these results are cached. View caching has the following characteristics:

  • The view must be one of the following types:

    • A standard view (a view created with the CREATE ... VIEW statement)

    • An inline view specified in the FROM clause of a SELECT statement

    • An inline view created with the WITH clause

  • The result of a view query with a correlated column (a reference to an outer query block) cannot be cached.

  • Query results are stored in the server result cache, not the client result cache.

  • A caching view is not merged into its outer (or referring) query block.

    Adding the RESULT_CACHE hint to inline views disables optimizations between the outer query and inline view to maximize reusability of the cached result.

Example 15-7 shows a query of the inline view view1.

Example 15-7 Using the RESULT_CACHE HInt Specified in Inline View

SELECT *
  FROM ( SELECT /*+ RESULT_CACHE */ department_id, manager_id, count(*) count
           FROM hr.employees 
          GROUP BY department_id, manager_id ) view1
 WHERE department_id = 30;

In this example, the SELECT statement from view1 is the outer block, whereas the SELECT statement from employees is the inner block. Because the RESULT_CACHE hint is specified only in the inner block, the results of the inner query are stored in the server result cache, but the results of the outer query are not cached.

Assume that the same session run a query of the view view2 as shown in Example 15-8.

Example 15-8 Using the RESULT_CACHE Hint Specified in WITH View

WITH view2 AS
( SELECT /*+ RESULT_CACHE */ department_id, manager_id, count(*) count
    FROM hr.employees 
   GROUP BY department_id, manager_id ) 
SELECT *
  FROM view2 
 WHERE count BETWEEN 1 and 5;

In this example, because the RESULT_CACHE hint is specified only in the query block in the WITH clause, the results of the employees query are eligible to be cached. Because these results are cached from the query in Example 15-7, the SELECT statement in the WITH clause in Example 15-8 can retrieve the cached rows.

15.3.2 Using Result Cache Table Annotations

You can also use table annotations to control result caching. Table annotations affect the entire query, not query segments. The primary benefit of using table annotations is avoiding the necessity of adding result cache hints to queries at the application level. Because a table annotation has a lower precedence than a SQL result cache hint, you can override table and session settings by using hints at the query level.

Table 15-4 describes the valid values for the RESULT_CACHE table annotation.

Table 15-4 Values for the RESULT_CACHE Table Annotation

Value Description

DEFAULT

If at least one table in a query is set to DEFAULT, then result caching is not enabled at the table level for this query, unless if the RESULT_CACHE_MODE initialization parameter is set to FORCE or the RESULT_CACHE hint is specified. This is the default value.

FORCE

If all the tables of a query are marked as FORCE, then the query result is considered for caching. The table annotation FORCE takes precedence over the RESULT_CACHE_MODE parameter value of MANUAL set at the session level.


This section describes how to use the RESULT_CACHE table annotations and contains the following topics:

15.3.2.1 Using the DEFAULT Table Annotation

The DEFAULT table annotation prevents the database from caching results at the table level.

Example 15-9 shows a CREATE TABLE statement that uses the DEFAULT table annotation to create a table sales and a query of this table.

Example 15-9 Using the DEFAULT Table Annotation

CREATE TABLE sales (...) RESULT_CACHE (MODE DEFAULT);

SELECT prod_id, SUM(amount_sold)
  FROM sales 
 GROUP BY prod_id 
 ORDER BY prod_id;

In this example, the sales table is created with a table annotation that disables result caching. The example also shows a query of the sales table, whose results are not considered for caching because of the table annotation.

See Also:

Oracle Database SQL Language Reference for information about the CREATE TABLE statement and its syntax

15.3.2.2 Using the FORCE Table Annotation

The FORCE table annotation forces the database to cache results at the table level.

Using the sales table created in Example 15-9, assume that you decide to force result caching for this table, you can do so by using the FORCE table annotation.

Example 15-10 shows an ALTER TABLE statement that uses the FORCE table annotation on the sales table.

Example 15-10 Using the FORCE Table Annotation

ALTER TABLE sales RESULT_CACHE (MODE FORCE);

SELECT prod_id, SUM(amount_sold)
  FROM sales 
 GROUP BY prod_id 
HAVING prod_id=136;

SELECT /*+ NO_RESULT_CACHE */ * 
  FROM sales
 ORDER BY time_id DESC;

This example includes two queries of the sales table. The first query, which is frequently used and returns few rows, is eligible for caching because of the table annotation. The second query, which is a one-time query that returns many rows, uses a hint to prevent result caching.

15.4 Monitoring the Result Cache

To view information about the server and client result caches, query the relevant database views and tables.

Table 15-5 describes the most useful views and tables for monitoring the result cache.

Table 15-5 Views and Tables with Information About the Result Cache

View/Table Description

V$RESULT_CACHE_STATISTICS

Lists various server result cache settings and memory usage statistics.

V$RESULT_CACHE_MEMORY

Lists all the memory blocks in the server result cache and their corresponding statistics.

V$RESULT_CACHE_OBJECTS

Lists all the objects whose results are in the server result cache along with their attributes.

V$RESULT_CACHE_DEPENDENCY

Lists the dependency details between the results in the server result cache and dependencies among these results.

CLIENT_RESULT_CACHE_STATS$

Stores cache settings and memory usage statistics for the client result caches obtained from the OCI client processes. This statistics table contains entries for each client process that uses result caching. After the client processes terminate, the database removes their entries from this table. The client table contains information similar to V$RESULT_CACHE_STATISTICS.

DBA_TABLES, USER_TABLES, ALL_TABLES

Contains a RESULT_CACHE column that shows the result cache mode annotation for the table. If the table is not annotated, then this column shows DEFAULT. This column applies to both server and client result caches.


Example 15-11 shows a query of the V$RESULT_CACHE_STATISTICS view to monitor server result cache statistics.

Example 15-11 Querying the V$RESULT_CACHE_STATISTICS View

COLUMN name FORMAT a20
SELECT name, value
  FROM V$RESULT_CACHE_STATISTICS;

The output of this query might look like the following:

NAME                          VALUE
--------------------     ----------
Block Size (Bytes)             1024
Block Count Maximum            3136
Block Count Current              32
Result Size Maximum (Blocks)    156
Create Count Success              2
Create Count Failure              0
Find Count                        0
Invalidation Count                0
Delete Count Invalid              0
Delete Count Valid                0

Example 15-12 shows a query of the CLIENT_RESULT_CACHE_STATS$ table to monitor the client result cache statistics.

Example 15-12 Querying the CLIENT_RESULT_CACHE_STATS$ View

SELECT stat_id, SUBSTR(name,1,20), value, cache_id
  FROM CLIENT_RESULT_CACHE_STATS$
 ORDER BY cache_id, stat_id;

The output of this query might look like the following:

STAT_ID    NAME OF STATISTICS      VALUE   CACHE_ID
=======    ==================      =====   ========
    1      Block Size               256         124
    2      Block Count Max          256         124
    3      Block Count Current      128         124
    4      Hash Bucket Count       1024         124
    5      Create Count Success      10         124
    6      Create Count Failure       0         124
    7      Find Count                12         124
    8      Invalidation Count         8         124
    9      Delete Count Invalid       0         124
   10      Delete Count Valid         0         124

The CLIENT_RESULT_CACHE_STATS$ table contains statistics entries for each active client process performing client result caching. Every client process has a unique cache ID.

To find the client connection information for the sessions performing client caching: 

  1. Obtain the session IDs from the CLIENT_REGID column in the GV$SESSION_CONNECT_INFO view that corresponds to the CACHE_ID column in the CLIENT_RESULT_CACHE_STATS$ table.

  2. Query the relevant columns from the GV$SESSION_CONNECT_INFO and GV$SESSION views.

For both server and client result cache statistics, a database that is optimized for result caching should show relatively low values for the Create Count Failure and Delete Count Valid statistics, while showing relatively high values for the Find Count statistic.

See Also:

Oracle Database Reference for information about these views and tables