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Creating an Oracle Database

原创 Linux操作系统 作者:v_fantasy 时间:2009-02-27 15:27:38 0 删除 编辑



Specifying the Shared Pool Size

The SHARED_POOL_SIZE initialization parameter is a dynamic parameter that lets you specify or adjust the size of the shared pool component of the SGA. Oracle Database selects an appropriate default value.

In releases before Oracle Database 10g Release 1, the amount of shared pool memory that was allocated was equal to the value of the SHARED_POOL_SIZE initialization parameter plus the amount of internal SGA overhead computed during instance startup. The internal SGA overhead refers to memory that is allocated by Oracle during startup, based on the values of several other initialization parameters. This memory is used to maintain state for different server components in the SGA. For example, if the SHARED_POOL_SIZE parameter is set to 64MB and the internal SGA overhead is computed to be 12MB, the real size of shared pool in the SGA is 64+12=76MB, although the value of the SHARED_POOL_SIZE parameter is still displayed as 64MB.Starting with Oracle Database 10g Release 1, the size of internal SGA overhead is included in the user-specified value of SHARED_POOL_SIZE. In other words, if you are not using the automatic shared memory management feature, then the amount of shared pool memory that is allocated at startup is exactly equal to the value of SHARED_POOL_SIZE initialization parameter. In manual SGA mode, this parameter must be set so that it includes the internal SGA overhead in addition to the desired value of shared pool size. In the previous example, if the SHARED_POOL_SIZE parameter is set to 64MB at startup, then the available shared pool after startup is 64-12=52MB, assuming the value of internal SGA overhead remains unchanged. In order to maintain an effective value of 64MB for shared pool memory after startup, you must set the SHARED_POOL_SIZE parameter to 64+12=76MB.

The Oracle Database 10g migration utilities recommend a new value for this parameter based on the value of internal SGA overhead in the pre-upgrade environment and based on the old value of this parameter. In Oracle Database 10g, the exact value of internal SGA overhead, also known as startup overhead in the shared pool, can be queried from the V$SGAINFO view. Also, in manual SGA mode, if the user-specified value of SHARED_POOL_SIZE is too small to accommodate even the requirements of internal SGA overhead, then Oracle generates an ORA-371 error during startup, along with a suggested value to use for the SHARED_POOL_SIZE parameter.When you use automatic shared memory management in Oracle Database 10g, the shared pool is automatically tuned, and an ORA-371 error would not be generated by Oracle.


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