How to set up sga in oracle

Oracle database is a relational database management system widely used in the industry, and its performance and reliability have been widely recognized. However, in order for the Oracle database to perform better, a series of configurations and optimizations are required, one of which is setting up the SGA (System Global Area).

SGA is the memory area used by Oracle database. It contains a variety of different memory components, such as Buffer Cache, Shared Pool, Java Pool, etc. Correctly setting up SGA can effectively improve database performance, especially in large-scale concurrent environments.

Below I will briefly introduce how to set up the SGA of the Oracle database.

Step one: Calculate the size of SGA

Before setting up SGA, we need to calculate the size of SGA first. It can be calculated by the following formula:

SGA size = db_block_size * db_cache_size

       shared_pool_size +
       java_pool_size +
       log_buffer

Among them, db_block_size represents the size of the database block, usually 8KB or 16KB; db_cache_size represents the size of the Buffer Cache, which can be determined according to the database The size and access mode are adjusted; shared_pool_size represents the size of Shared Pool, usually set to 20%~30% of the total memory; java_pool_size represents the size of Java Pool, which can be adjusted according to whether Java programs are used in the database; log_buffer represents the log cache Size, usually set to 64KB or 128KB.

For example, if our database block size is 8KB, Buffer Cache size is 2GB, Shared Pool size is 512MB, Java Pool size is 256MB, and log cache size is 128KB, then the calculated SGA size is:

SGA size = 8KB * 2GB 512MB 256MB 128KB = 2.75GB

Step 2: Modify SGA parameters

After calculating the SGA size, you can start setting the SGA parameters . The specific steps are as follows:

1. Log in to the database and use sysdba permissions.
2. Execute the following command to view the size and parameters of the current SGA:

select * from v$sga;

3. Modify parameters:

a. db_cache_size

To modify the size of the Buffer Cache, you can modify it through the following command:

alter system set db_cache_size = 2G scope = spfile;

Here will be The size of the Buffer Cache is set to 2GB.

b. shared_pool_size

To modify the size of Shared Pool, you can modify it through the following command:

alter system set shared_pool_size = 512M scope = spfile;

Here the Shared Pool size is set to 512MB.

c. java_pool_size

To modify the size of Java Pool, you can modify it through the following command:

alter system set java_pool_size = 256M scope = spfile;

Here the Java Pool size is set to 256MB.

d. log_buffer

To modify the size of the log buffer, you can use the following command to modify it:

alter system set log_buffer = 128K scope = spfile;

Here the log cache size is set to 128KB.

4. Exit the session.

Step 3: Restart the database

After modifying the SGA parameters, you need to restart the database to take effect. You can restart with the following command:

shutdown immediate;
startup;

After restarting, you can check the size and parameters of SGA again to ensure that the modification is successful.

Summary

SGA is a very important concept in Oracle database. Database performance can be significantly improved by correctly setting SGA. In actual operation, it is necessary to calculate the SGA size based on the actual situation of the database, and set parameters according to actual needs. At the same time, the database needs to be backed up before modifying parameters to prevent data loss or damage.

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