关于PGA的大小
作者：vogts | 分类： 大话技术 | 标签： 大话技术 | 日期：2008-06-02
前几天MSN上有个朋友的数据库PGA设置了4G，忽然整个os里，PGA占了10多个G。这个问题我一直耿耿于怀，记得Donny曾经说过，今天终于在聊天记录找到了。
“In the latest release 10.2 Oracle changed these default values. The memory allocated to a single SQL operator (_smm_max_size) is limited to:
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for P_A_T <= 500MB the parameter _smm_max_size = 20% of P_A_T
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for P_A_T between 500MB and 1000MB the parameter _smm_max_size = 100M
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for P_A_T betweeen 1001MB and 2560MB (2.5GB) the parameter _smm_max_size = 10% of P_A_T
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for P_A_T > 2560MB (2,5GB) the parameter _smm_max_size = 262,060 MB (~0,25GB)
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I have seen even cases when these values were even bigger after the instance was restarted with P_A_T set at 4GB.
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The maximum value for parallel operations changed from 30% to 50% PGA_AGGREGATE_TARGET/DOP. Also the DOP changed. When DOP <=5 then _smm_max_size is used, otherwise _smm_px_max_size/DOP limits the maximum memory usage. .
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不要把PGA设置的太大了，否则确实有这样的问题。
原文URL： http://www.dba-oracle.com/oracle_news/2005_12_19_10g_release_changes.htm
