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Background documentation OMS Heap Locate the document in the library structure

Note

The OMS heap is only used by SAP liveCache database instances.

In addition to the data cache and the converter, during operation liveCache database instances also use a private OMS cache in the main memory: the OMS heap.

The OMS heap grows when additional heap memory is requested. You can configure the maximum size of the OMS heap with the OMS_HEAP_LIMIT liveCache database parameter.

The OMS heap contains the following data:

·        Local copies of OMS data

When an object within a consistent view is accessed for the first time, the database system writes the corresponding data to the OMS heap.

·        Local application data

The database system copies the data of each OMS version to the OMS heap when it is read.

To access a persistent object, the database system searches first in the OMS heap. If it does not find the object there, it searches in the data cache. If it does not find the object there either, the database system copies the object from the data area to the data cache, and from there to the OMS heap. The database system then makes all changes to the object in the OMS heap.

Any objects that are read but not changed within a consistent view are deleted from the OMS heap by the database system.

When a transaction ends (COMMIT), the database system writes the OMS data from the OMS heap to the data cache.

Note

Configure the general database parameter CACHE_SIZE and the liveCache parameter OMS_HEAP_LIMIT in such a way that prevents swapping at the operating system level.

See also:

Concepts of the Database System,

·        General Database Parameters

·        liveCache Database Parameter

Database Administration in CCMS: SAP liveCache Technology

·        Structure linkHeap Usage

·        Structure linkMonitoring the Main Memory Areas

 

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