ITPub博客

首页 > 应用开发 > IT综合 > Specifying the Shared Pool Size (111)

Specifying the Shared Pool Size (111)

原创 IT综合 作者:tsinglee 时间:2008-01-02 13:43:53 0 删除 编辑

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.

[@more@]

来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/10599713/viewspace-996322/,如需转载,请注明出处,否则将追究法律责任。

请登录后发表评论 登录
全部评论
  • 博文量
    740
  • 访问量
    1922978