Oracle Concepts - Guidelines for Tuning the Oracle Shared Pool

Oracle Tips by Burleson Consulting

In Summary

I hope you now understand that the old "just increase the shared pool" answer isn't good enough anymore when it comes to tuning problems. You must take an in depth look at your shared pool and tune what needs to be tuned, not just throw memory at a problem until it submerges. Indeed, I have shown that in some cases increasing the size of the shared pool may harm performance and decreasing the size may be advisable. The shared pool is vital to the proper performance of your Oracle database, you must have it properly tuned or drown in bad performance. Next we will cover what to pin, the shared pool and multi-threaded server, hashing and generalized library and dictionary cache tuning. We have also discussed ways to monitor for what objects should be pinned, discussed multi-threaded server, looked at hashing problems and their resolution as well as examined classic library and data dictionary cache tuning. We have established 8 guidelines for tuning the Oracle shared pool:

Guideline 1: If gross usage of the shared pool in a non-ad-hoc environment exceeds 95% (rises to 95% or greater and stays there) establish a shared pool size large enough to hold the fixed size portions, pin reusable packages and procedures. Gradually increase shared pool by 20% increments until usage drops below 90% on the average.

Guideline 2: If the shared pool shows a mixed ad-hoc and reuse environment, establish a shared pool size large enough to hold the fixed size portions, pin reusable packages and establish a comfort level above this required level of pool fill. Establish a routine flush cycle to filter non-reusable code from the pool.

Guideline 3: If the shared pool shows that no reusable SQL is being used establish a shared pool large enough to hold the fixed size portions plus a few megabytes (usually not more than 40) and allow the shared pool modified least recently used (LRU) algorithm to manage the pool. (also see guideline 8)

Guideline 4: Determine usage patterns of packages, procedures, functions and cursors and pin those that are frequently used.

Guideline 5: In Oracle7when using MTS increase the shared pool size to accommodate MTS messaging and queuing as well as UGA requirements. In Oracle8 use the Large Pool to prevent MTS from effecting the shared pool areas.

Guideline 6: Use bind variables, PL/SQL (procedures or functions) and views to reduce the size of large SQL statements to prevent hashing problems.

Guideline 7: In a system where there is no flushing increase the shared pool size in 20% increments to reduce reloads and invalidations and increase object cache hit ratios.

Guideline 8: In any shared pool, if the overall data dictionary cache miss ratio exceeds 1 percent, increase the size of the shared pool.

Using these guidelines and the scripts and techniques covered in this lesson, your should be well on the way towards a well tuned and well performing shared pool.

Table 18: Initialization Parameters That Effect The Shared Pool

NAME	DESCRIPTION
shared_pool_size	size in bytes of shared pool (7 and 8)
shared_pool_reserved_size	size in bytes of reserved area of shared pool (7 and 8)
shared_pool_reserved_min_alloc	minimum allocation size in bytes for reserved area of shared pool (7 and 8)
large_pool_size	size in bytes of the large allocation pool (8 only)
parallel_max_servers	Maximum number of parallel query slaves, if set forces calculation and setting of large pool size parameter (8i)
parallel_adaptive_multi_user	If set forces calculation of large pool size is over-ridden if size manually set(8i). Oracle DOES NOT recommend setting parallel_adaptive_multi_user.
parallel_automatic_tuning	If set forces calculation of large pool size is over-ridden if size is manually set (8i)
large_pool_min_alloc	minimum allocation size in bytes for the large allocation pool (8 only, obsolete in 8i)
parallel_min_message_pool	minimum size of shared pool memory to reserve for pq servers (8 only, obsolete in 8i)
backup_io_slaves	Number of backup IO slaves to configure (8 only)
temporary_table_locks	Number of temporary table locks to configure (7 and 8)
dml_locks	Number of DML locks to configure (7 and 8)
sequence_cache_entries	Number of sequence numbers to cache (7 and 8)
row_cache_cursors	Number of row caches to set up (7 and 8)
max_enabled_roles	Number of role caches to set up (7 and 8)
mts_dispatchers	Number of MTS dispatcher processes to start with (7 and 8)
mts_max_dispatchers	Maximum number of dispatcher processes to allow (7 and 8)
mts_servers	Number of MTS servers to start with (7 and 8)
mts_max_servers	Maximum number of MTS servers to allow (7 and 8)
open_cursors	Maximum number of open cursors per session (7 and 8)
Cursor_space_for_time	Hold open cursors until process exits (7 and 8)

Table 19: Initialization Parameters Used In Tuning Shared Pool

VIEW NAME	PURPOSE
V$PARAMETER	Contains current settings for all documented initialization parameters
V$SGASTAT	Contains sizing information for all SGA areas
V$SQLAREA	Contains information and statistics on the SQL area of the shared pool
V$DB_OBJECT_CACHE	Contains information on all cached objects in the database shared pool area
V$LIBRARYCACHE	Contains statistics on the library caches
V$ROWCACHE	Contains statistics on the data dictionary caches
DBA_USERS	Contains database user information
V$BUFFER_POOL	Oracle8 view showing pool areas
V$BUFFER_POOL_STATISTICS	Oracle8 buffer pool statistics
V$BH	View that monitors every buffer in buffer pool

Table 20: Views Dealing With Shared Pool and Buffer Tuning

Software	Manufacturer	Purpose
Oracle Administrator	RevealNet, Inc.	Administration Knowledge base
Q Diagnostic	Savant, Corp.	Provide Oracle DB diagnostics

Table 21: Software Mentioned in Lessons

This is an excerpt from the eBook "Oracle DBA made Simple".

For more details on Oracle database administration, see the "Easy Oracle Jumpstart" by Robert Freeman and Steve Karam. It?s only $19.95 when you buy it directly from the publisher here.

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