Large Pool

Oracle Instance : What is Large Pool

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http://dbaspot.com/oracle-database-administration/oracle-administration/oracle-instance-what-large-pool-251.html 

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.

1. Session memory for the a shared server and the Oracle XA Interface when distributed transactions are involved
2. I/O Server Processes
3. Parallel Query Buffers
4. 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

Using the Large Pool

http://download.oracle.com/docs/cd/B19306_01/server.102/b14211/memory.htm#i52838

Unlike the shared pool, the large pool does not have an LRU list. Oracle does not attempt to age objects out of the large pool.
You should consider configuring a large pool if your instance uses any of the following:

·         Parallel query

Parallel query uses shared pool memory to cache parallel execution message buffers.

·         Recovery Manager

Recovery Manager uses the shared pool to cache I/O buffers during backup and restore operations. For I/O server processes and backup and restore operations, Oracle allocates buffers that are a few hundred kilobytes in size.

·         Shared server

In a shared server architecture, the session memory for each client process is included in the shared pool.