Oracle memory structure-SGA

The Oracle memory structure is an important part of the Oracle database system. The following describes the SGA memory structure in the Oracle memory structure, which is helpful to you.

SGA is a group of shared memory structures allocated to the system. It can contain data or control information of a database instance. If multiple users connect to the same database instance, data in the instance's SGA can be shared by multiple users. When the database instance is started, the SGA memory is automatically allocated. When the database instance is closed, the SGA memory is recycled. SGA is the region with the largest memory usage and an important factor affecting database performance.

The SGA area can be read and written. All users logging on to the instance can read the information in SGA. When oracle performs an operation, the service process writes the modified information to SGA.

SGA mainly includes the following data structures:

Buffer Cache)

Redo Log Buffer)

Shared Pool)

Java Pool)

Large Pool)

Stream Pool Streams Pool --- 10 Gb later)

Data Dictionary Cache)

Other information, such as database and instance status information)

 
 

  
  
SQL> show sga  
  
  
 
  
  
Total System Global Area 612368384 bytes  
  
  
 
  
  
Fixed Size 1250428 bytes  
  
  
 
  
  
Variable Size 192940932 bytes  
  
  
 
  
  
Database Buffers 411041792 bytes  
  
  
 
  
  
Redo Buffers 7135232 bytes  
 
 

The data dictionary cache and other information in SGA will be accessed by the background process of the instance. They will be fixed in SGA after the instance is started and will not change, so this part is also called fixed SGAFixed SGA ). The size of these regions is generally less than 100 kb.

The size of the Shared Pool, Java Pool, Large Pool, and Streams Pool is changed based on the corresponding system parameter settings. Therefore, it is called the variable SGAVariable SGA ).
 

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