Large Pool & Java Pool

Oracle Large Pool is an optional memory component of the oracle database SGA. This area is used for providing large memory allocations in many situations that arise during the operations of an oracle database instance.

• Session memory for the a shared server and the Oracle XA Interface when distributed transactions are involved
• I/O Server Processes
• Parallel Query Buffers
• Oracle Backup and Restore Operations using RMAN

 Large Pool plays an important role in Oracle Database Tuning since the allocation of the memory for the above components otherwise is done from the shared pool. Also due to the large memory requirements for I/O and Rman operations, the large pool is better able to satisfy the requirements instead of depending on the Shared Pool Area.

Usage of a Large Pool Area allows the shared pool to primarily cache SQL and avoid the overhead casued by shrinking the SQL Cache Area.

This area is only used if shared server architecture, also called multi-threaded server (MTS), is used, or if parallel query is utilized. The large pool holds the user global areas when MTS is used and holds the parallel query execution message queues for parallel query.

By issuing a summation select against the v$sgastat view, a DBA can quickly determine the size of the large pool area currently being used.

SELECT name, SUM(bytes) FROM V$SGASTAT WHERE pool='LARGE POOL' GROUP BY ROLLUP(name);

The select above should be used when an "ORA-04031: Unable to allocate 16084 bytes of shared memory  large pool unknown object large pool hea PX large pool error is received with a configured large pool the number of bytes specified may differ

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