Large Pool And JAVA Pool

Large Pool : 

Large Pool is an optional area in SGA. It relieves the burden of the Shared pool also.

It provides an area of memory from which large allocations can be made. Oracle's backup and restore utilities typically allocate buffers that are hundreds of kilobytes in size. These will be allocated in the large pool if the large pool memory allocation is present.

Large Pool Reduces the overhead of the shared pool, in case of shared server connection mode.

A large Pool is used for the following :

• Session memory for the shared server and the Oracle XA Interface when distributed transactions are involved
• I/O server processes
• Backup and restore operations for RMAN
• Parallel execution message buffers

              PARALLEL_AUTOMATIC_TUNING set to TRUE

Large Pool does not use an LRU list. It is sized by LARGE_POOL_SIZE and can be resized dynamically.

For shared server or parallel query buffers, Oracle uses the shared pool primarily for caching shared SQL statements. For a shared server or parallel query buffers, Oracle Uses the large pool memory when we set below Parameter value to TRUE.

PARALLEL_AUTOMATIC_TUNING=TRUE

Allocating session memory from the large pool for a shared server or parallel query buffers, Thus relieving the burden on the area within the shared pool.

By allocating session memory from the large pool for shared SQL, the database avoids performance overhead caused by increasing and shrinking the shared SQL cache in shared pool memory.

By allocating memory in large buffers for RMAN operations, I/O server processes, and parallel buffers, the large pool can satisfy large memory requests better than the shared pool.

By allocating memory form the large pool, for caching SQL parse tree in favor of shared server session information, I/O, and backup and recovery processes, The shared pool does not have to give up own memory for these processes. So the Performance gain happens from the reduction of overhead from increasing and shrinkage of the shared SQL cache in the shared pool.

The multi-threaded server will also take advantage of the large pool, allocating session memory there instead of in the shared pool, thus leaving more of the shared pool open for SQL statements and execution plans.

Below is t use Cases of Large Pool:

Backup And Restore :

Recovery Manager (RMAN) uses the large pool when the parameter set as below.

• BACKUP_DISK_IO = n
• BACKUP_TAPE_IO_SLAVE = TRUE

If the large pool is configured but is not large enough, the allocation of memory from the large pool fails. RMAN writes an Error message to the alert log file and does not use I/O slaves for backup and restore.

Parallel Execution :

Large Pool is used for Parallel execution when the below parameter is set to TRUE, Otherwise,  these buffers are allocated and use the shared pool memory.

PARALLEL_AUTOMATIC_TUNING=TRUE

Sizing The LARGE POOL :

A large pool area will only be available if the parameter has set in the initialization parameter. For example, to allocate a large pool of 10 megabytes, you would add the following line to your database's initialization parameter file.

LARGE_POOL_SIZE = 10M

The large pool is sized in bytes defined by the LARGE_POOL_SIZE  Parameter. This Parameter can be dynamically resized using the ALTER SYSTEM SET command.

ALTER SYSTEM SET LARGE_POOL_SIZE=50M;

Large Pool and LRU List :

The large Pool does not have an LRU list.  It is different from reserved space in the shared pool, which uses LRU List.

JAVA POOL :

The java pool is a RAM region within the Oracle SGA and the java pool RAM is used to provide:

• Services Parsing of Java code and scripts. 
• Installation tasks related to Java applications with Oracle versions. 
• Java stored procedure code parsing.
• Sized by JAVA_POOL_SIZE Parameter

The JAVA pool is an optional setting but is required if you are installing and using JAVA. Its Size is set in Bytes using the JAVA_POOL_SIZE. The Default Size of the JAVA POOL  is 24MB (Oracle 9i)

Thank You !!