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https://issues.apache.org/jira/browse/HBASE-6137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13429319#comment-13429319
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Lars Hofhansl commented on HBASE-6137:
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I missed this one when I filed HBASE-6505.
Not sure I understand when exactly the start/stop methods would be called.
> RegionServer-level context and start/stop life-cycle methods for observer
> coprocessor
> -------------------------------------------------------------------------------------
>
> Key: HBASE-6137
> URL: https://issues.apache.org/jira/browse/HBASE-6137
> Project: HBase
> Issue Type: New Feature
> Components: coprocessors
> Affects Versions: 0.94.0
> Reporter: James Taylor
>
> Coprocessors are a great way for an application to affect server-side
> processing. We're using observer coprocessors via the postScannerOpen to
> enable a scan to do aggregation. There's currently no way, however, to
> store/share state across coprocessor invocations on the regions within a
> region server. Ideally, we'd like to be able to have a context object that
> allows state to be shared across coprocessor invocation for the regions on
> the same region server. This would save us the setup cost for "compiling" our
> aggregators again for each region. Also useful, would be:
> - a start/stop method invocation on this new region server context object
> before the first region invocation and after the last region invocation on a
> given region server.
> - a way to pass state to the start/stop method from the client. The
> scan.setAttribute works well for passing state for the invocation on each
> region, but ideally something that would allow state to be passed just once
> per region server. One use case would be to pass a cache of the row data for
> a hash join implementation, where we wouldn't want to pass this information
> for every region.
> Our current work around is to either take the hit of the extra setup costs
> for the coprocessor invocation on each region or use an Endpoint coprocessor
> to initialize state prior to the client scan that will cause coprocessor
> invocations.
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