Introduction to the global zone of Oracle10g Management System

Do you know the actual application of the global zone (SGA) of Oracle10g Management System? Are you familiar with the operation of some of its related steps? If you are interested in the global partition (SGA) of the Oracle10g management system, you can browse our articles.

There are several parameters that affect the SGA memory allocation quantity. Except for SGA_MAX_SIZE, the other parameters are dynamic parameters, that is, the parameters that can be dynamically modified using the alter system statement during database operation. the size of SGA is dynamic. By modifying these parameters, it can be SGA increase or decrease.

SGA component and SGA memory Particles

It is composed of many memory components, which are memory pools used to meet specific memory allocation requests. for example, in a shared pool (used to buffer disk data blocks), all shards allocate and recycle memory space with the smallest memory unit, oracle tracks memory unit allocation and usage of shards within the system.

The memory of SGA is allocated by particles, and the size of particles is determined by the size of SGA. generally, on most platforms, if SGA is smaller than or equal to 1G, the size of the particles is 4 MB. If SGA is greater than 1G, the size of the particles is 16 MB, the difference is that on a 32-bit Windows platform, when the size of SGA is greater than 1 GB, the size of particles is 8 MB rather than 16 MB. For more information, see the operating system documentation.

You can use the V $ SGAINFO system to view the size of particles used by an instance. The same size is used for dynamic components of all SGA instances.

If the size of the specified SGA component is not an integer multiple of the particle size, Oracle returns an integer multiple of the size rounded to the SGA memory component. instead of the specified size. for example, if the particle size is 4 MB and you set the DB_CACHE_SIZE parameter to 10 MB, the actually allocated memory will be 12 MB.

Limit the size of SGA

The SGA_MAX_SIZE parameter specifies the maximum number of SGA instances in the life cycle of the instance. dynamically modify the Buffer cache, shared pool, large pool, java pool, and streams pool size affected by these parameters, and the total size of SGA. but it cannot exceed the value set by the SGA_MAX_SIZE parameter.

If not specified, the sum of all memory components specified in the initialization parameters is used as the default value.

Use automatic shared memory management

Use the SGA_TARGET parameter to enable automatic shared memory management. previously, shared memory components such as java_pool and large_pool are automatically managed. In addition, you must ensure that the STATISTICS_LEVEL initialization parameter is set to TYPICAL (default) or ALL.

The SGA_TARGET initialization parameter reflects the size of the SGA.

Table 2-3 automatically allocates the size of the SGA component and corresponding parameters.

SGA component initialization parameters

The global zone (SGA) of the Oracle10g management system is unavailable within the fixed SGA and other Oracle database instances.

Shared Pool SHARED_POOL_SIZE

Large pool LARGE_POOL_SIZE

Java pool JAVA_POOL_SIZE

Buffer high cache DB_CACHE_SIZE

Table 2-4 SGA components for manually allocating sizes using SGA_TARGET Space

SGA component initialization parameters

Log buffer LOG_BUFFER

The keep and recycle buffer caches DB_KEEP_CACHE_SIZE

DB_RECYCLE_CACHE_SIZE

Non-standard buffer high cache block size DB_nK_CACHE_SIZE

STREAMS_POOL_SIZE

Run the following SQL query in manual management mode to obtain the SGA_TARGET value.

SELECT (

(Select sum (value) from v $ SGA )-

(SELECT CURRENT_SIZE from v $ SGA_DYNAMIC_FREE_MEMORY)

) "SGA_TARGET"

From dual;

Then you can delete the initialization parameters of the shared memory automatically managed by Oracle.

For example, in the manual management mode, you can set the SGA_MAX_SIZE to 1200 M:

SHARED_POOL_SIZE = 200 M

DB_CACHE_SIZE = 500 M

LARGE_POOL_SIZE = 200 M

The above content is an introduction to the global zone (SGA) of the Oracle10g management system.