Library Cache Hit Ratio (LibGetHitRatio)

The LibGetHitRatio parameter reports the percentage of all attempts to lock library cache entries that were immediately successful.

The LibGetHitRatio parameter is calculated based on the delta values of sga_library_cache_gets,
sga_library_cache_gethits, which are pulled from the Oracle database's V$LIBRARYCACHE table. The values are stored in Oracle as accumulative values, that is, the values continue to increase from the time the instance was started.
The values are pulled from the database each time the parameter polls the database (collects the data). The values are stored in variables. Every time the parameter polls, the difference between the new value received from the database for sga_library_cache_gets, sga_library_cache_gethits and the old values of sga_library_cache_gets, sga_library_cache_gethits. These delta values are then used in the standard LibGetHitRatio formula, identifies when the LibGetHitRatio is low or high at a certain time in the day.

Recommendations

• Increase the init.ora shared_pool_size parameter. Increasing the shared pool size reduces implicit reparsing of SQL statements and PL/SQL blocks on execution.
• If needed, increase the init.ora open_cursors parameter to increase the number of cursors permitted for a session. This action takes advantage of additional memory available for shared SQL areas.
• Whenever possible, use stored procedures and identical SQL statements in applications so they can share a SQL area.

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