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Donald K. Burleson

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Oracle SGA

The redo buffers contain row change information, transaction commit history, and checkpoint history. This data is written into the redo logs and eventually to the archive logs. A commit will force a disk write, as will the filling of a redo log buffer or the reaching of a predefined checkpoint.

For Oracle7 the queue and request areas store data that is being transferred between processes such as servers and other Oracle7 processes. The shared SQL area stores all SQL statements in a parsed form. When a user or process issues an SQL (Structured Query Language) command, the shared SQL area is checked to see if the command already exists in parsed form; if it does, this shared version is used. If the multithreaded server option is utilized, some of the user Process Global Area (PGA; described in the next section) is also placed in the shared pool. Under Oracle8, the LARGE POOL area is an optional extension to the SGA. If configured via its initialization parameters, the LARGE POOL takes over the session-level memory needs for MTS (multithreaded server) or XA sessions. The LARGE POOL is also used for I/O slaves and during Oracle backup and restore operations. Under Oracle8i, parallel execution queues are also allocated from the LARGE POOL area. If you will be using the parallel query option, pay particular attention to the section in Chapter 12, Tuning Oracle Applications, on tuning the shared, large, and Java pools for Oracle8i. In Oracle, the database buffer areas are allowed to have multiple blocksizes; this promises greater tuning flexibility for mixed-mode databases.

Oracle PGA

PGA stands for Process Global Area. This is memory reserved for each process that uses Oracle. It contains the context area. Oracle sets this area’s size based on the values of the initialization parameters:
 

This is an excerpt by Mike Ault’s book “Oracle Administration & Management”.  If you want more current Oracle tips by Mike Ault, check out his new book “Mike Ault’s Oracle Internals Monitoring & Tuning Scripts” or Ault’s Oracle Scripts Download.

 

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