ORACLE database system global zone

System Global Area
SGA (System Global Area) is a set of shared buffer storage areas allocated by the ORACLE system for instances. It is used to store database data and control information to achieve the management and operation of database data. Figure 2-3 shows The relationship between the instance and SGA and database.
SGA is divided into the following parts:
(1) Shared pool.
(2) Data block buffer.
(3) Log buffer.
(4) Dictionary buffer.
The following are introduced respectively:
 Note:
The size of SGA should be less than half of the physical memory.
In the ORACLE system, all data exchanges between users and the ORACLE database system must pass through the SGA area.
1. Shared Pool
consists of a shared SQL area and a data dictionary area. The parameter shared_pool_size determines the size of the shared pool. The shared SQL area includes:
(1) The text of the SQL or PL/SQL statement.
(1) Syntax analysis form of SQL or PL/SQL statement.
(2) Execution plan of SQL or PL/SQL statement.
 Note: shared_pool_size=physical memory × (15~20)% is the lower limit for OPS.
2. Data block buffer
is used to store data read from data files. Its size is determined by the following two parameters:
DB_BLOCK_SIZE determines the size of the data block, generally 2K or 4K.
DB_BLOCK_BUFFERS determines the number of data blocks.
DB_BUFFERS=DB_BLOCK_BUFFERS×DB_BLOCK_SIZE=physical memory×(15～25)%, take the upper limit for OPS. This value should be as large as possible.
3. Log buffer
Backs up the modified buffer blocks in the database buffer in the form of record items, and these record items will be written to the log file. The size of the log buffer is determined by the parameter LOG_BUFFER
4. The dictionary buffer
is used to store data dictionary information lines.
5. General principles for SGA setting size
When setting various parameters to adjust the SGA size, ensure that it is less than half of the physical memory.
The calculation method of SGA is as follows:
SGA=DB_BLOCK_BUFFERS×DB_BLOCK_SIZE+SHARE_POOL_SIZE+SORT_AREA_SIZE+1M+3×DB_BLOCK_SIZE×(CPUs+2)×PARALELL_MAX_SREVERS
 Note:
OPS only has the last item.
SORT_AREA_SIZE: Sorting area, the number of concurrent users is large, the value should be large when sorting is required.
PARALELL_MAX_SREVERS: 2×Number of CPUs×4×Number of concurrent users. This value cannot be modified for a single CPU.

The above is the global area of ​​the ORACLE database system. For more related articles, please pay attention to the PHP Chinese website (www.php.cn)!