[
https://issues.apache.org/jira/browse/HBASE-10015?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13830498#comment-13830498
]
Lars Hofhansl commented on HBASE-10015:
---------------------------------------
Here's another idea:
* we already lock the RegionScannerImpl.next/seek/reseek, etc.
* what if we pass the RegionScannerImpl instance as a lock object to
StoreScanner
* in updateReaders() we'd then lock on that RegionScannerImpl instance, or we'd
call a special synchronized method in RegionScannerImpl and have it update the
readers.
The lock scope would be broader, but it should be correct, and it would allow
us to remove all locking from StoreScanner.
I'll experiment with that.
> 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
> Fix For: 0.98.0, 0.96.1, 0.94.15
>
> Attachments: 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.
--
This message was sent by Atlassian JIRA
(v6.1#6144)
