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https://issues.apache.org/jira/browse/HBASE-26784?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17502914#comment-17502914
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Bryan Beaudreault commented on HBASE-26784:
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Thanks for merging [~Xiaolin Ha] !
> Use HIGH_QOS for ResultScanner.close requests
> ---------------------------------------------
>
> Key: HBASE-26784
> URL: https://issues.apache.org/jira/browse/HBASE-26784
> Project: HBase
> Issue Type: Improvement
> Reporter: Bryan Beaudreault
> Assignee: Bryan Beaudreault
> Priority: Major
> Fix For: 2.5.0, 2.6.0, 3.0.0-alpha-3
>
>
> Active scanners take resources on the RegionServer, and scanner leaks can
> have a big impact on GC. Under high load, ResultScanner.close() calls might
> get rejected or timed out before executing. Exceptions thrown by close() are
> currently swallowed, so clients will not retry. This leads to a leak of
> active scanners on the server side.
> These calls should be relatively free to execute, and executing them will
> free up the resources which can have an impact on overall RegionServer
> performance. As such it can be beneficial to execute all
> ResultScanner.close() requests with HIGH_QOS regardless of the priority of
> the underlying Scan.
> In a scan-heavy stress test I ran, after a couple minutes the Full GC time
> (using G1GC) starts increasing and we start seeing 1s pauses, due to
> increasing number of active scanners (into the 10s of thousands). Re-running
> the stress test with HIGH_QOS for ResultScanner.close() eliminates the leak
> and GC time remains stable.
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