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In the Space user menu you can see, among other things, the sizes of the most important caches, the number of accesses to these caches, and the cache hit rates since the last time the Database Monitoring function was started.

Procedure

Open the DBA Cockpit (transaction DBACOCKPIT) and select   Space   Caches  .

Result

The system displays information about the size and general efficiency of the caches of the database. In a balanced system, the hit rate for the data cache is more than 99 %, for the catalog cache more than 90 %. The lower the hit rate, the lower the efficiency of your database system.

Cache Sizes

Size of the I/O buffer cache (data cache, converter and other caches)

Cache Accesses

Statistical information about accesses to the data cache (SAP liveCache technology: accesses to links to undo log entries for the objects (History/Undo), the OMS data (OMS Data), and SQL data (SQL Data)), catalog cache, and sequence cache

Data cache usage

Usage information for the data cache (SAP liveCache technology: usage of the areas for SQL data (SQL Data), OMS data (OMS Data), and the links to undo log entries for the objects (History/Undo))

Cache-Specific Parameter Settings

CacheMemorySize: Size of the I/O buffer cache

CAT_CACHE_SUPPLY: Size of the catalog cache

The I/O buffer cache (with its main component, the data cache) should be configured large enough that the greatest possible amount of data you require for normal operation of your SAP system can be stored in the data cache. Otherwise, the data is written to the data area, which negatively affects database performance. If necessary, change the size of the I/O buffer cache by setting the general database parameter CacheMemorySize.

For SAP systems with special requirements, a higher data cache hit rate may also be necessary (such as SAP NetWeaver BI).

Comments About SAP liveCache Technology

The I/O buffer cache, and therefore the data cache as well, must be dimensioned so that it can hold all OMS data, links to undo log entries, and SQL data in the data cache. Otherwise, the data is written to the data area, which negatively affects SAP liveCache performance.

The memory of the data cache should take up about 40% of the main memory available to the SAP liveCache database. You may need to adjust its size to the requirements of the application.

More information: Database Administration in CCMS, Monitoring the Main Memory Area

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