ORACLE parent latch和children latch
About parent vs child latches. There is no fundamental low level difference between parent and child latches, they are all small regions of memory modified with atomic test-and-set style opcodes.
You see parent (and solitary) latches from x$ksllt where kslltcnm = 0 and child latches have Kslltcnm > 0 (their child number is stored there).
V$LATCH_PARENT shows all latches with kslltcnm 0, V$LATCH_CHILDREN shows all latches with cnm > 0. V$LATCH just summarizes & groups all statistics up using the latch number, it doesn't care about parent vs child latches.
It's up to Oracle, how it uses the child and parent latches, normally when child latches are used, parent latches don't get used much (or at all), since all resources to be protected have been spread between child latches already.
今天看到书中讲LATCH的时候提到了两个视图V$LATCH_CHILDREN和V$LATCH_PARENT ，不太清楚两者的区别，去百度了一下，还没百度到，GOOGLE了才找到一篇相关的文章。
看了上面的讲解，我个人理解就是二者其实没什么区别，完全取决于ORACLE如何使用。
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