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Spotlight on SAP ASE 2.11 - Release Notes

Package Cache graph

If the overall package cache hit rate for the database is low, this graph tells you whether the selected application is contributing to the problem.

About package cache

Package cache is memory that temporarily stores package and section information required for the execution of static and dynamic SQL statements in the database. Caching packages allows the database manager to reduce its internal overhead by eliminating the need to access the system catalog when reloading a package. Likewise, caching dynamic SQL information eliminates the need to compile the statement. In general, caching the section for a static or dynamic SQL statement can improve performance, especially when the same statement is used multiple times by the application.

Sections are held in package cache until one of the following occurs:

  • The database is shut down

  • The package or dynamic SQL statement is invalidated

  • The cache runs out of space

The graph

The Package Cache graph contains a single series, Hit rate, which plots the percentage of package cache lookups at the application level that were satisfied by data already residing in the package cache. If this hit rate is high, the cache is performing effectively for the application. A smaller ratio indicates that the application is performing more reads directly from the system catalog than from the package cache and might therefore be contributing to the overall low hit rate for the database.

The graph title area shows the number of package cache inserts and lookups that occurred for the application during the last monitoring interval.

For related statistical information

The Statistics tab contains entries for all package cache statistical counts used to generate this graph. The names for these statistics begin with Package Cache. These statistics are derived from the PKG_CACHE data elements that the DB2 snapshot monitor captures at the application level.


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