Oracle Memory Structures

My teacher often ask in every lecture.. Explain oracle memory structure and explain different SGA Buffers. Every time i was asked about different pools i mix up, So finally i decide to write them on my blog so that i can quickly refresh them.

Oracle Memory Structure

Oracle Memory Structure:
The oracle memory structure associated with Oracle instance include.
1. System Global Area (SGA)
2. Program Global Area (PGA)


1. System Global Area (SGA)
SGA Include data structures
1.1 Database buffer cahce:  Cache blocks of data retrieved from the database.
1.2 Redo log Buffer:  This buffer stores redo information (if you instance crash then recovery process can be initiated using this buffer)
1.3 Shared Pool: This pool caches various constructs that can be shared amount different DB users
1.4 Large Pool: This is an optional pool that provide large memory space to the processes that require large memory like Oracle Backup and Recovery Operations.
1.5 Java Pool: Is used for all session-specific Java Code and data within the Java Virtual Machine (JVM)
1.6 Streams Pool:  Is used by oracle streams to copy one data file to other location/files.


How to Check Memory Allocated for the SGA?
When Oracle instance is started using Enterprise Manager or SQL*Plus, the amount of memory allocated to SGA is displayed.

2. Program Global Area (PGA)
PGA is a memory region that contains data and control information for each server process. When an oracle client connect to an oracle server a PGA is allocated to that client.