Oracle memory structure, oracle Structure

Oracle memory structure, oracle Structure

The memory structure of Oracle is divided into SGA and PGA. SGA is dynamically allocated. It is configured by the sga_max_size parameter and allocated when the oracle database instance is started, share an SGA for all session connections; For PGA, each user creates a PAG memory zone for session connections.

 

Shared Pool: stores the execution structure (Execution Plan) of the recently executed SQL statement that has been defined (data dictionary). It mainly consists of library cache and data dictionary cache. The size parameter is shared_pool_size.

 

Library cache mainly stores shared SQL area and shared pl/SQL area.

 

Data dictionary cache is mainly used to store data systems, dynamic performance views of systems, and system tables.

 

The major concern of SGA is that database buffer cache is mainly used to store data blocks of data files. It directly stores the data read from the hard disk in the memory, improving the data operation speed. For user operations on data, the first step is to find the data in the database buffer cache. If you can find the data, the data will be directly returned and will not be found from the hard disk, improving the data response speed. An important indicator reflecting database performance is the hit rate of database buffer cache. The main parameters include db_keep_cache_size, db_cache_size, and db_recycle_cache_size.

 

Redo log buffer: it is the cache of the redo log of the data file. If you need to recover data and read the redo log file, the database operation records will be read from the redo log buffer first. The Operation Records of the database are first written to the redo log buffer, and then stored in the data file redo log files.

 

Larger pool: When Rman is backed up, the larger pool is used for data caching. Some server procees I/O operations also need to use the larger pool for data caching.

 

Java pool: The size is determined by the java_pool_size parameter. For Methods written in the java language in oracle, java pool is used during execution. This cache area is mainly used for java-related operations.

 

 

 

 

Brief description of the memory structure of the oracle Database System

Memory is an important factor affecting database performance. Oracle8i uses static memory management, and Oracle uses dynamic memory for 10 Gb.
Memory Management. Static Memory Management means that in the database system, no matter whether a user is connected or not
A fixed amount of memory is allocated as long as the database service is running. Dynamic Memory Management allows
Modify the memory size during running, use large memory when reading big data blocks, use small memory when reading small data blocks, and read
Use the standard memory settings when getting standard memory blocks.
According to the system's memory usage, the memory of the Oracle database can be divided into the following parts:
?? System Global zone: SGA (System Global Area)
?? Program Global zone: PGA (Programe Global Area)
?? Sorting pool: (Sort Area)
?? Large Pool: (Large Pool)
?? Java Pool: (Java Pool)

Brief description of the memory structure of the oracle Database System

1: Oracle Instance)
On a server, every running Oracle database is associated with a database instance.
Means of accessing the database.
The instance is identified by ORACLE_SID in the operating system and INSTANCE_NAME in Oracle,
The two values are the same. When the database is started, the system first allocates the system global zone (SGA) in the server memory ),
The Oracle memory structure is formed, and several operating system processes with resident memory are started.
Process structure. The memory area and the background process are collectively called an Oracle instance.
The relationship between the database and the instance is 1-to-1/n. In a non-parallel database system, each Oracle Database
Instances correspond to each other. In a parallel database system, a database corresponds to multiple instances.
When an instance fails, other instances automatically serve to ensure normal database operation. In any
In this case, each instance can correspond to only one database.

2: Oracle 10 Gb dynamic memory management
Memory is an important factor affecting database performance. Oracle8i uses static memory management, and Oracle uses dynamic memory for 10 Gb.
Memory Management. Static Memory Management means that in the database system, no matter whether a user is connected or not
A fixed amount of memory is allocated as long as the database service is running. Dynamic Memory Management allows
Modify the memory size during running, use large memory when reading big data blocks, use small memory when reading small data blocks, and read
Use the standard memory settings when getting standard memory blocks.
According to the system's memory usage, the memory of the Oracle database can be divided into the following parts:
• System Global zone: SGA (System Global Area)
• Program Global zone: PGA (Programe Global Area)
• Sorting pool: (Sort Area)
• Large Pool: (Large Pool)
• Java Pool: (Java Pool)

2-1: System Global Area (SGA)
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.
You can use the following statement to query the SGA information. The size of sga_max_size cannot be dynamically adjusted.
============================================
SQL> show parameter sga
NAME TYPE VALUE
-------------------------------------------------------
Lock_sga boolean FALSE
Pre_page_sga boolean FALSE
Sga_max_size big integer 164 M
Sga_target big integer 0

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