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https://issues.apache.org/jira/browse/HBASE-15716?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15358754#comment-15358754
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Hiroshi Ikeda commented on HBASE-15716:
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That's bad. When there is no scanner, it is possible that only
getSmallestReadPoint is repeatedly called, creating new nodes without GC
because of chaining from tailRef. That's headaching and I'll think more next
week.
> HRegion#RegionScannerImpl scannerReadPoints synchronization constrains random
> read
> ----------------------------------------------------------------------------------
>
> Key: HBASE-15716
> URL: https://issues.apache.org/jira/browse/HBASE-15716
> Project: HBase
> Issue Type: Bug
> Components: Performance
> Reporter: stack
> Assignee: stack
> Attachments:
> 15716.implementation.using.ScannerReadPoints.branch-1.patch,
> 15716.prune.synchronizations.patch, 15716.prune.synchronizations.v3.patch,
> 15716.prune.synchronizations.v4.patch, 15716.prune.synchronizations.v4.patch,
> 15716.wip.more_to_be_done.patch, HBASE-15716.branch-1.001.patch,
> HBASE-15716.branch-1.002.patch, HBASE-15716.branch-1.003.patch,
> HBASE-15716.branch-1.004.patch, HBASE-15716.branch-1.005.patch,
> ScannerReadPoints.java, Screen Shot 2016-04-26 at 2.05.45 PM.png, Screen Shot
> 2016-04-26 at 2.06.14 PM.png, Screen Shot 2016-04-26 at 2.07.06 PM.png,
> Screen Shot 2016-04-26 at 2.25.26 PM.png, Screen Shot 2016-04-26 at 6.02.29
> PM.png, Screen Shot 2016-04-27 at 9.49.35 AM.png, Screen Shot 2016-06-30 at
> 9.52.52 PM.png, Screen Shot 2016-06-30 at 9.54.08 PM.png,
> TestScannerReadPoints.java, before_after.png,
> current-branch-1.vs.NoSynchronization.vs.Patch.png, hits.png,
> remove.locks.patch, remove_cslm.patch
>
>
> Here is a [~lhofhansl] special.
> When we construct the region scanner, we get our read point and then store it
> with the scanner instance in a Region scoped CSLM. This is done under a
> synchronize on the CSLM.
> This synchronize on a region-scoped Map creating region scanners is the
> outstanding point of lock contention according to flight recorder (My work
> load is workload c, random reads).
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