Shared Pool

The shared pool is an area of Oracle memory that includes two main structures:

• The library cache, which stores parsed SQL and PL/SQL statements
• The dictionary cache, which stores the Oracle data dictionary (or Oracle metadata)

The SHARED_POOL_SIZE parameter is defined in the INIT.ora or INIT<SID>.ora file and is used to regulate the size of the shared pool. Set the SHARED_POOL_SIZE parameter to a minimum of 3500000 (3.5 million). Setting the shared pool to a smaller value can degrade performance, forcing Oracle to do disk I/O to retrieve objects that cannot fit in the shared pool. A larger shared pool may be required, depending on the size and number of models and the number of users.

Buffer Cache

The buffer cache serves as a memory cache for all data going to and from Oracle data files. When Oracle needs a block of data it first checks whether that block exists in the buffer cache. If it does, Oracle gets the data from the buffer cache�avoiding disk access. Having a large enough buffer cache lets the Oracle server bypass most I/O requests.

Buffer cache size is controlled by the DB_BLOCK_BUFFERS parameter defined in the INIT.ora or INIT<SID>.ora file. Set the buffer cache to a minimum of 4 MB. Values smaller than 4 MB force Oracle to do many more I/O requests and significantly degrades the performance. Values larger than 4 MB improve performance and should be used if memory is available.

Note: In Oracle, the DB_BLOCK_BUFFERS parameter is specified as a number of database blocks instead of actual size in bytes. To compute the value of DB_BLOCK_BUFFERS, divide the desired buffer cache size in bytes by the database block size defined by the DB_BLOCK_SIZE parameter in the INIT.ora or INIT<SID>.ora file.