Bryan Beaudreault created HBASE-26784:
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Summary: 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
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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