ORACLE STRUCTURES

Oracle Database server structures:

1.memory structures

2.process structures

3.stroage structures

 

Oracle Database system:

1.Oracle Database

2.database instance

•System Global Area(SGA)

•Shared Pool   : Caches various constructs that can be shared among users

• Library cache
• Shared SQL area

• Data dictionary cache
• Control structures

 

•Database buffer cache  :Caches blocks of data retrieved from the database

Is part of the SGA

Holds copies of data blocks that are read from data files

Is shared by all concurrent  users

 

•KEEP buffer pool : A specialized type of database buffer cache that is tuned to    retain blocks of data in memory for long periods of time

 

•RECYCLE buffer pool : A specizlied tyoe of database buffer cache that is tuned to recycle or remove block from memory quickly

 

•nK buffer cache  : One of several specialized database buffer caches designed to hold block size different than the default database block size

 

•Redo log buffer  : Caches redo information(used for instance recovery) until it can be written to the physical redo log files stored on the disk

Is a circular buffer in the SGA

Holds information about chages made to the database

Contains redo entries that have the information to redo chages made by operations such as DML and DLL

 

•Large pool  : Optional raea that provides large memory allocations for certain large process,such as Oracle backup and recovery operations,and I/O server process

Session memeory for the shared server and the Oracle XA interface

I/O server processes

Oracle Database backup and restore operations

 

•Java pool  : Used for all session-specific java code and data in the Java Virtual Machine(JVM)

Java pool memory is used to store all session-specific Java code and data in the JVM

 

•Stream pool  : Used by Oracle Streams to stroe information required by capture and apply

Streams pool memory is used exclusively by Oracle Streams to:

• Store buffered queue messages
• Provide memory for Oracle Streams processes

 

•Program Global Area(PGA)

•stack space

•user global area(UGA)

Cursor area for storing runtime information about a session

User session data storage area for control information about session

SQL working areas for processing SQL statements consiting of :

• A sort area for functions that order data such as ORDER BY and GROUP BY
• A hash area for performing hash joins of tables
• A create bitmap area used in bitmap index creatiion common to data warehouses
• A bitmap merge area used for resolving bitmap index plan execution