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sql 语句中or条件之种种情况
1、相同字段or条件，转换为inlist 走index range scanSQL> select * from test_or a 2 where a.object_id=20 or a.object_id=21;执行计划----------------------------------------...
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minimum heap size for ibm jvm
When you have established the maximum heap size that you need, you might want to set the minimum heap size to the same value; for example, -Xms 512M -Xmx 512M. Using the same values is not usually a g...
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Frequently asked questions about the Garbage Collector
What are default values for the native stack (-Xss) and Java stack (-Xoss)? The Native stack size is machine-dependent, because it is based on the platform's C stack usage. The Java stack size is 400...
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Dynamic Sampling 两种方式的利弊
There are two ways to use dynamic sampling: TheOPTIMIZER_DYNAMIC_SAMPLING parameter can be set at the databaseinstance level and can also be overridden at the session level with theALTER SESSION co...
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我的SQL调优公式T＝S/V
比较愚钝，从事调优工作这么些年，处理过的性能问题也不少，也就总结出这么个公式来S指sql所需访问的资源总量，V指sql单位时间所能访问的资源量，T自然就是SQL执行所需时间了这个公式很简单，调优的目标是减少T...
