Donald K. Burleson Oracle Tips

Pinning the Oracle packages with start-up triggers

Package pinning has become a very important part of Oracle tuning, and with the introduction of system-level triggers in Oracle8i, we now have an easy tool to ensure that frequently-executed PL/SQL remains cached inside the shared pool.

Just like using the KEEP pool with the data buffer caches, the pinning of packages ensures that the specified package always remains in the Most-recently-used (MRU) end of the data buffer.  This prevents the PL/SQL from being paged-out, and then re-parsed upon reload.  The Oracle DBA controls the size of this RAM region by setting the shared_pool_size parameter to a value large enough to hold all of the PL/SQL.

Pinning of packages involves two areas:

• Pinning frequently executed packages – Oracle performance can be greatly enhanced by pinning frequently executed packages inside the SGA.

• Pinning the standard Oracle packages – These are shown in the code listing below, and should always be opined to prevent re-parsing by the Oracle SGA.

You can interrogate the v$db_object_cache view to see the most frequently used packages, and automatically pin them at database start-up time (with an ON DATABASE STARTUP trigger) using dbms_shared_pool.keep.

create or replace trigger

   pin_packs

       after startup on database

       begin

       dbms_shared_pool.keep('DBMS_ALERT');                                 

       dbms_shared_pool.keep('DBMS_DDL');

       dbms_shared_pool.keep('DBMS_DESCRIBE');

       dbms_shared_pool.keep('DBMS_LOCK');                         

       dbms_shared_pool.keep('DBMS_OUTPUT');

       dbms_shared_pool.keep('DBMS_PIPE');

       dbms_shared_pool.keep('DBMS_SESSION');                          

       dbms_shared_pool.keep('DBMS_SHARED_POOL');

       dbms_shared_pool.keep('DBMS_STANDARD');

       dbms_shared_pool.keep('DBMS_UTILITY');                                  

       dbms_shared_pool.keep('STANDARD');

       end;

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