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https://issues.apache.org/jira/browse/HBASE-19047?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16220038#comment-16220038
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Duo Zhang commented on HBASE-19047:
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What if a user just opens a new RegionScanner and return it and then close the
one you passed in? This may be done by calling instanceof on the returned
RegionScanner, but what if user wraps it before returning it?
And I think RegionScanner is way too complicated to implement by a CP users, so
maybe just like the Region/Store way? You can give me a Region/Store, but I can
safely cast it to HRegion/HStore as I'm sure there is no other implementation.
The only exception is InternalScanner, which we allow user to do wrapping.
Thanks.
> CP exposed Scanner types should not extend Shipper
> --------------------------------------------------
>
> Key: HBASE-19047
> URL: https://issues.apache.org/jira/browse/HBASE-19047
> Project: HBase
> Issue Type: Sub-task
> Components: Coprocessors
> Reporter: Anoop Sam John
> Assignee: Anoop Sam John
> Fix For: 2.0.0-alpha-4
>
> Attachments: HBASE-19047.patch, HBASE-19047_V2.patch,
> HBASE-19047_V2.patch
>
>
> Shipper is a IA.Private interface and very much internal..
> Right now CP exposed RegionScanner is extending this and so exposing the
> shipped() method. This by mistake is called, can harm the correctness of the
> cells in the Results.
> preScannerOpen() allowing to return a new Scanner is also problematic now.
> This can allow users to create a Region scanner from Region and then wrap it
> and return back (Well same can be done by postScannerOpen also), it can so
> happen that the wrapper is not implementing the shipped() properly. In any
> way exposing the shipped () is problematic.
> Solution Steps
> 1. Remove preScannerOpen() , the use case I can think of is wrapping the
> original scanner. The original scanner can be created by Region.getScanner
> way only.. May be no need to remove this hook. Just remove the ability for
> it to return a RegionScanner instance. Call this with the Scan object and
> the CP can change the Scan object if they want.
> 2. Let RegionScanner not extending Shipper but only RegionScannerImpl
> implements this
> 3. We have ref to the RegionScanner created by core and let that be used by
> RegionScannerShippedCallBack when the post hook doing a wrap.
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