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Automatic Shared Memory Management (73)

原创 IT综合 作者:tsinglee 时间:2007-10-23 10:36:06 0 删除 编辑

In previous database releases, a database administrator (DBA) was required to
manually specify different SGA component sizes by setting a number of initialization
parameters, including the SHARED_POOL_SIZE, DB_CACHE_SIZE, JAVA_POOL_SIZE, and LARGE_POOL_SIZE
parameters. Oracle Database 10g includes the Automatic Shared Memory Management feature which
simplifies the SGA memory management significantly. In Oracle Database 10g, a DBA can simply specify
the total amount of SGA memory available to an instance using the SGA_TARGET initialization
parameter and the Oracle Database will automatically distribute this memory among
various subcomponents to ensure most effective memory utilization.

Setting a single parameter greatly simplifies the administration task. You
specify only the amount of SGA memory that an instance has available and forget about the sizes of
individual components. No out of memory errors are generated unless the system has
actually run out of memory.
Automatic SGA management can enhance workload performance without requiring
any additional resources or manual tuning effort. With manual configuration of the
SGA, it is possible that compiled SQL statements frequently age out of the shared pool
because of its inadequate size. This can increase the frequency of hard parses, leading
to reduced performance. When automatic SGA management is enabled, the internal
tuning algorithm monitors the performance of the workload, increasing the shared
pool if it determines the increase will reduce the number of parses required

assm : Automatic Shared Memory Management 自动共享内存管理
指定sga_target参数后 , Oracle自动在sga组件之间调整大小 , 使内存更有效利用 。

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