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https://issues.apache.org/jira/browse/HBASE-27402?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17611914#comment-17611914
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Bryan Beaudreault commented on HBASE-27402:
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Actually, this problem does not exist in master because it does not exist in
AsyncTable. AsyncTable already clones the scan object. So this patch would just
be for Table in branch-2, if accepted.
> Clone Scan in ClientScanner to avoid errors with Scan re-used
> -------------------------------------------------------------
>
> Key: HBASE-27402
> URL: https://issues.apache.org/jira/browse/HBASE-27402
> Project: HBase
> Issue Type: Improvement
> Reporter: Bryan Beaudreault
> Priority: Major
>
> This has come up before in https://issues.apache.org/jira/browse/HBASE-1774
> and https://issues.apache.org/jira/browse/HBASE-4891. The major pushback was
> around ScanMetrics, which relied on sharing a mutable Scan object.
> Since https://issues.apache.org/jira/browse/HBASE-17584, ScanMetrics are
> available on ResultScanner and the method on Scan was deprecated (removed in
> master).
> I think this issue became pretty urgent in
> https://issues.apache.org/jira/browse/HBASE-17167, when we started passing
> mvcc into the Scan object. If a user unknowingly reuses the Scan object, this
> can seem like data loss since the Scan will return none of the expected data.
> We recently hit this in our upgrade from hbase client 1.2 to 2.4.6, where
> use-cases that had worked in 1.2 suddenly started returning no results in
> 2.4.6. It's very hard to debug.
> I suggest that we now add the clone in master branch. For branch-2, I think
> we could put it behind a config param to preserve backwards compatibility of
> Scan.getScanMetrics. If the config param is enabled, scan cloning occurs and
> Scan.getScanMetrics will be inaccurate. Personally I think this is far better
> scenario, because data result accuracy is more important than metrics. But we
> can leave it to the user to decide, and provide a release note.
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