Donald K. Burleson
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.
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
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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