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https://issues.apache.org/jira/browse/HBASE-10015?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13829403#comment-13829403
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Lars Hofhansl commented on HBASE-10015:
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Thanks [~vrodionov], we'll look at RegionScanner next. :) My evil plans is to
eventually get rid of all synchronization during scanning and provide exclusion
by containment instead.
The overall improvement is real. Validated on various different machines. The
effect of memory stalls is probably more pronounced in the running server.
In any case, I think we agree that this patch can't make things worse (provide
it is correct, of course).
I also tried with count(*) queries in Phoenix on tall tables (to rule out some
anomalies with Filters). I see a 90% improvement there - again only on tall
tables.
> 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,
> 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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