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Keep Buffer Pool & Recycle Buffer Pool

Posted by FatDBA on December 9, 2012

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Let’s discuss about two of lesser known sections in Database Buffer Cache named: Keep Buffer Pool and Recycle Buffer Pool.

Keep Buffer Pool
Data which is frequently accessed should be kept in Keep buffer pool. Keep buffer pool retains data in the memory. So that next request for same data can be entertained from memory. This avoids disk read and increases performance. Usually small objects should be kept in Keep buffer. DB_KEEP_CACHE_SIZE initialization parameter is used to create Keep buffer Pool. If DB_KEEP_CACHE_SIZE is not used then no Keep buffer is created. Use following syntax to create a Keep buffer pool of 40 MB. Often times an application will have a few very critical objects, such as indexes, that are small enough to fit in the buffer cache but are quickly pushed out by other objects. This is the perfect case for using the initialization
parameter called DB_KEEP_CACHE_SIZE. The KEEP buffer pool is aptly named. It is intended to be used for objects that take absolute priority in the cache. For instance, critical indexes or small look-up tables.
DB_KEEP_CACHE_SIZE=40M

Recycle Buffer Pool
Blocks loaded in Recycle Buffer pool are immediate removed when they are not being used. It is useful for those objects which are accessed rarely. As there is no more need of these blocks so memory occupied by such blocks is made available for others data. The RECYCLE buffer pool is best utilized to “protect” the default buffer pool from being consumed by randomly accessed blocks of data.

For example if ASM is enabled then available memory can be assigned to other SGA components . Use following syntax to create a Recycle Buffer Pool

DB_RECYCLE_CACHE_SIZE=20M

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