Limiting the Size of the SGA (96)

最新推荐文章于 2025-12-17 14:20:19 发布

转载最新推荐文章于 2025-12-17 14:20:19 发布 · 96 阅读

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#数据库

本文详细介绍了Oracle数据库中SGA_MAX_SIZE参数的作用及其设置原则。该参数用于限定整个实例运行周期内系统全局区的最大尺寸，并可以动态调整部分SGA组件的大小，但总体不超过SGA_MAX_SIZE所设定的值。

The SGA_MAX_SIZE initialization parameter specifies the maximum size of the System
Global Area for the lifetime of the instance. You can dynamically alter the initialization
parameters affecting the size of the buffer caches, shared pool, large pool, Java pool,
and streams pool but only to the extent that the sum of these sizes and the sizes of the
other components of the SGA (fixed SGA, variable SGA, and redo log buffers) does not
exceed the value specified by SGA_MAX_SIZE.

If you do not specify SGA_MAX_SIZE, then Oracle Database selects a default value that
is the sum of all components specified or defaulted at initialization time. If you do
specify SGA_MAX_SIZE, and at the time the database is initialized the value is less
than the sum of the memory allocated for all components, either explicitly in the
parameter file or by default, then the database ignores the setting for SGA_MAX_SIZE.

限制SGA的大小
1. 当oracle初始化启动时,如果sga_max_size的值小于显式的指定的各sga组件值之和,则oracle将
会忽略sga_max_size
2. 当oracle初始化启动时,如果sga_max_size小于sga_target时,启动之后,sga_max_size将等于
sga_target
3. 启动之后,sga_target就不能大于sga_max_size.

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