Modify oracle sga

Oracle's SGA (System Global Area) is a memory area shared by all processes. It stores a large number of important data structures, such as cache, lock, connection and so on. The size of SGA directly affects the performance of Oracle database. If SGA is set too small, it will not be able to accommodate the data needed by all processes, resulting in frequent disk reading and writing and a large number of I/O operations, which will further affect the response time of queries and transactions. If the setting is too large, it will take up too much memory resources, leading to the downtime of the operating system.

Therefore, for an Oracle database in a production environment, a reasonable SGA setting is very important. This article will discuss how to modify Oracle SGA.

Confirm the current size of SGA Use the following query statement in the SQL*Plus command line interface:

SHOW PARAMETER SGA_TARGET;

You can view the size of the current SGA_TARGET parameter. This value specifies the SGA target size of Oracle, in bytes. It should be noted that this value may be different from the actual memory size allocated to SGA. Therefore, we also need to get the actual SGA size through the following query statements:

SELECT * FROM V$SGA;

After executing this statement, the current SGA will be output, in which the Size column shows the total size of SGA.

Calculating the required SGA size Before modifying SGA, we need to calculate the required SGA size first. This process needs to consider many factors, such as database size, number of connections, cache hit rate, concurrency and so on. Here, we use a simple formula to calculate a preliminary SGA size:

SGA = (DB_BLOCK_SIZE * DB_BLOCK_BUFFERS) + SHARED_POOL_SIZE + LARGE_POOL_SIZE + JAVA_POOL_SIZE + PGA_AGGREGATE_TARGET

Where DB_BLOCK_SIZE is the size of each data block, DB_BLOCK_BUFFERS is the number of blocks in the data block buffer, SHARED_POOL_SIZE is the size of shared pool, LARGE_POOL_SIZE is the size of large pool and variable pool, JAVA_POOL_SIZE is the size of Java pool, and PGA_AGGREGATE_TARGET is the PGA target size. The values of these parameters can be obtained by querying the V$PARAMETER table. It should be noted that the value of DB_BLOCK_BUFFERS should be a power of 2, and its value should satisfy: SGA+PGA+ other memory.