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Oracle11g新特性之Auto Memory Management

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Jun 07, 2016 pm 03:12 PM

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欢迎进入Oracle社区论坛，与200万技术人员互动交流 >>进入 Auto Memory Management是Oracle10g提出来的一个新特性，在最新的Oracle11g数据库中又得到了进一步的发展。通过使用自动内存管理，Oracle数据库中的PGA和SGA内存之间可以互相转换，根据当前的工作负

欢迎进入Oracle社区论坛，与200万技术人员互动交流 >>进入

Auto Memory Management是Oracle10g提出来的一个新特性，在最新的Oracle11g数据库中又得到了进一步的发展。通过使用自动内存管理，Oracle数据库中的PGA和SGA内存之间可以互相转换，根据当前的工作负载来自动设定Oracle内存区域中的PGA和SGA的大小。这种间接的内存转换依赖于操作系统的共享内存的释放机制来获得内部实例的调优。目前这种技术可以应用于Linux, Solaris, HPUX, AIX 和Windows等操作系统上。

首先我们来回顾下Oracle10g的自动内存管理特性。在Oracle10g的数据库中，只有SHARED_POOL_SIZE、DB_CACHE_SIZE、LARGE_POOL_SIZE、JAVA_POOL_SIZE、STREAMS_POOL_SIZE五个SGA组件可以被自动调整，其中PGA的最大值由初始化参数PGA_AGGREGATE_TARGET决定，SGA的最大值由初始化参数SGA_TARGET决定。

在Oracle11g数据库中，使用自动内存管理特性不再需要设定参数PGA_AGGREGATE_TARGET和SGA_TARGET，因为这两个参数都已经被修改成自动调优的，除非想指定PGA和SGA的最小值才需要设定这两个参数。在Oracle11g数据库中，则需要设置一个叫做MEMORY_TARGET的初始化参数，这个参数是指整个Oracle实例所能使用的内存大小，包括PGA和SGA的整体大小，在MEMORY_TARGET的内存大小之内，PGA和SGA所用的内存可以根据当前负载情况自动相互转换。如果当初始设定的MEMORY_TARGET的内存不够当前数据库使用的时候，Oracle11g还提供了另外一个初始化参数MEMORY_MAX_TARGET，当原始设定的内存不够使用的时候，可以手工来动态调节MEMORY_TARGET的大小，但是不允许超过MEMORY_MAX_TARGET的值。下面这张图简单明了的描述出了Oracle11g数据库内存大小的设定参数。

Oracle11g新特性之Auto Memory Management

此外，Oracle11g数据库还提供了几个用于监控自动内存管理的视图：

V$MEMORY_DYNAMIC_COMPONENTS：描述当前所有内存组件的状态

V$MEMORY_RESIZE_OPS：循环记录最后800次的SGA大小调整请求

X$KMGSTFR:循环记录最后800次的SGA的转换地址

_MEMORY_MANAGEMENT_TRACING=23:对于所有的内存转换调整行为均记录保存为跟踪文件

Oracle11g新特性之Auto Memory Management

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