Oracle Concepts - Guidelines for Tuning the Oracle Shared Pool

Oracle Concepts - Guidelines for Tuning the Oracle Shared Pool

In Summary

I hope you nowunderstand that the old "just increase the shared pool" answer isn'tgood enough anymore when it comes to tuning problems. You must take an in depthlook at your shared pool and tune what needs to be
tuned, not just throw memoryat a problem until it submerges. Indeed, I have shown that in some casesincreasing the size of the shared pool may harm performance and decreasing thesize may be advisable.  The shared pool is vital to the proper performanceof your
Oracle database, you must have it properly tuned or drown in badperformance. Next we will cover what to pin, the shared pool and multi-threadedserver, hashing and generalized library and dictionary cache tuning. We havealso discussed ways to monitor for what
objects should be pinned, discussedmulti-threaded server, looked at hashing problems and their resolution as wellas examined classic library and data dictionary cache tuning. We haveestablished 8 guidelines for tuning the Oracle shared pool:
Guideline 1: Ifgross usage of the shared pool in a non-ad-hoc environment exceeds 95% (risesto 95% or greater and stays there) establish a shared pool size large enough tohold the fixed size portions, pin reusable
packages and procedures. Graduallyincrease shared pool by 20% increments until usage drops below 90% on theaverage.
Guideline 2: Ifthe shared pool shows a mixed ad-hoc and reuse environment, establish a sharedpool size large enough to hold the fixed size portions, pin reusable packagesand establish a comfort level above this required
level of pool fill. Establisha routine flush cycle to filter non-reusable code from the pool.
Guideline 3: Ifthe shared pool shows that no reusable SQL is being used establish a sharedpool large enough to hold the fixed size portions plus a few megabytes (usuallynot 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 pinthose that are frequently used.
Guideline 5: InOracle7when using MTS increase the shared pool size to accommodate MTSmessaging and queuing as well as UGA requirements. In Oracle8 use the LargePool to prevent MTS from effecting the shared pool areas.
Guideline 6: Usebind variables, PL/SQL (procedures or functions) and views to reduce the sizeof large SQL statements to prevent hashing problems.
Guideline 7: In asystem where there is no flushing increase the shared pool size in 20%increments to reduce reloads and invalidations and increase object cache hitratios.
Guideline 8: Inany shared pool, if the overall data dictionary cache miss ratio exceeds 1percent, increase the size of the shared pool.
Using theseguidelines and the scripts and techniques covered in this lesson, your shouldbe 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: ViewsDealing 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: SoftwareMentioned in Lessons