HP ProLiant 3000 DSS Sizing and Tuning of Oracle8 for Windows NT on Compaq Ser - Page 23

DSS Sizing and Tuning of Oracle8 for Windows NT on CompaqServers Page 21 Memory Tuning System Global Area (SGA) Size Because the Oracle8 Server SGA resides in server memory, this is allocated at the startup of the instance. The SGA is made up of the following components: Fixed Size + Variable Size + DB Block Buffers + Redo Buffers = Size of SGA Fixed Size is determined by the Oracle products that you have installed. It is approximately 43K bytes. Variable Size is determined by init.ora parameters such as SHARED_POOL_SIZE and DB_BLOCK_LRU_LATCHES. DB Block Buffer is determined by the DB_BLOCK_BUFFERS*DB_BLOCK_SIZE parameters. NOTE: If you are using asynchronous I/O and Oracle can lock down memory for asynchronous I/O, the DB Block Buffers will not be swappable. Redo Buffer size is determined by the LOG_BUFFERS parameter plus approximately 80K bytes of overhead space. LOG_BUFFERS is specified in bytes. Program Global Area (PGA) Size The PGA is allocated by Oracle when a user thread connects and a session is created or for each Parallel Query thread. The PGA is a region of memory that contains data and control information for a single connection. This memory must be available at the connect time for a particular user, therefore the amount of free server memory is a limitation to the number of concurrent connections. The PGA's size is affected by the following parameters: • OPEN_LINKS • DB_FILES • LOG_FILES © 1998 Compaq Computer Corporation, All Rights Reserved Doc No ECG156/0398