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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-10015) Major performance improvement: Avoid synchronization in StoreScanner
Date Mon, 25 Nov 2013 04:03:35 GMT

    [ https://issues.apache.org/jira/browse/HBASE-10015?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13831165#comment-13831165
] 

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

Was just looking at making a trunk patch.
In trunk StoreScanners for compaction *do* register a change observer? But not in 0.94?!

So - sigh - the patch I just made for 0.94 will not work in trunk. And maybe more importantly:
Is there a lingering bug in 0.94?

> 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
>            Assignee: Lars Hofhansl
>         Attachments: 10015-0.94-new-sample.txt, 10015-0.94-v2.txt, 10015-0.94-v3.txt,
10015-0.94-v4.txt, 10015-0.94-withtest.txt, 10015-0.94.txt, 10015-trunk-v2.txt, 10015-trunk-v3.txt,
10015-trunk-v4.txt, 10015-trunk-v4.txt, 10015-trunk-v4.txt, 10015-trunk.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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