Oracle Memory Architecture (i)

Oracle Memory Architecture

The basic memory structures associated with Oracle instances include:

System global Area (SGA): shared by all server processes and background processes

Program Global Zone (PGA): dedicated by each server and background process, each with a PGA.

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The system global Area (SGA) is a shared memory area that contains data and control information for an instance, consisting of the following:

Database buffers cache (db buffer cache): used to cache data blocks retrieved from disk

Redo Log buffer (redo buffer): Used to cache redo information until it can be written to disk

Shared pools (Share pool): used to cache various structures that can be shared among users

Large pool: An optional region for buffering large I/O requests to support parallel queries, shared servers,

Backup operations such as Oracle XA and Rman

Java pool: Used to hold session-specific Java code and data in a Java Virtual machine (JVM)

Stream pool: Used by Oracle Streams

The size of the database buffer cache, shared pool, large pool, stream pool, and Java pool can be automated according to current requirements

Adjustment.

Granules: Define view 10g online documentation,

All SGA is allocate and deallocate space in units of granules. Oracle Database Tracks SGA memory use with internal numbers of granules for each SGA component.

That is, the basic unit of Oracle memory allocation, the size of the granules depends on the total SGA size, most platforms, if the total SGA is less than 1G, then granules is 4M, if more than 1G, then 16M.

Automatic Shared Memory Management (ASSM)

Automatic management of Shared memory (ASMM) is another key self-management enhancement in Oracle databases. This feature enables management automation of most important shared memory structures used by Oracle DB instances, easing the amount of manual configuration of these components. In addition to more efficient use of available memory, which reduces the cost of acquiring additional hardware memory resources, the ASMM feature introduces a more dynamic, flexible, and adaptable memory management solution that greatly simplifies the management of Oracle databases.

For example, for systems that run large online transaction processing (OLTP) jobs during the day (requiring large buffer caches) and running parallel batch jobs at night (which requires large pools of memory), you must configure both the buffer cache and the large pool to accommodate peak demand. With the ASMM feature, when an OLTP job runs, the buffer cache acquires most of the memory to ensure good I/O performance. When you start data Analysis and report batch jobs later, the memory is automatically ported to a large pool for parallel query operations, without a memory overflow error.

The structure of the SGA can be dynamically adjusted by setting the Sga_target, and the SGA components can be adjusted as follows:

Fixed SGA and other internal allocations needed by the Oracle Database instance

The log buffer

The shared pool

The Java Pool

The buffer cache

The Keep and recycle buffer caches (if specified)

nonstandard block size buffer caches (if specified)

The Streams Pool

sql> show parameter sganame                                   TYPE         VALUE------------------------------------ ----------- ------------------------------lock_sga                               boolean     falsepre_page _sga                          boolean     FALSEsga_max_size                           big integer 1500msga_target                            big integer 1500m

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Oracle Memory Architecture (i)