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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10015) Major performance improvement: Avoid synchronization in StoreScanner
Date Thu, 21 Nov 2013 06:49:37 GMT

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Lars Hofhansl commented on HBASE-10015:
---------------------------------------

One last note before I call it quits today.
The win appears to reduce the per row overhead by 50-60%. With 5 CQs this shrinks proportionally
to 10-15% or so.


> Major performance improvement: Avoid synchronization in StoreScanner
> --------------------------------------------------------------------
>
>                 Key: HBASE-10015
>                 URL: https://issues.apache.org/jira/browse/HBASE-10015
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>         Attachments: 10015-0.94-withtest.txt, 10015-0.94.txt, TestLoad.java
>
>
> Did some more profiling (this time with a sampling profiler) and StoreScanner.peek()
showed up a lot in the samples. At first that was surprising, but peek is synchronized, so
it seems a lot of the sync'ing cost is eaten there.
> It seems the only reason we have to synchronize all these methods is because a concurrent
flush or compaction can change the scanner stack, other than that only a single thread should
access a StoreScanner at any given time.
> So replaced updateReaders() with some code that just indicates to the scanner that the
readers should be updated and then make it the using thread's responsibility to do the work.
> The perf improvement from this is staggering. I am seeing somewhere around 3x scan performance
improvement across all scenarios.
> Now, the hard part is to reason about whether this is 100% correct. I ran TestAtomicOperation
and TestAcidGuarantees a few times in a loop, all still pass.
> Will attach a sample patch.



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