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From "Anoop Sam John (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-19047) CP exposed Scanner types should not extend Shipper
Date Tue, 24 Oct 2017 17:35:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-19047?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16217332#comment-16217332
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Anoop Sam John commented on HBASE-19047:
----------------------------------------

At this time of assign Shipper, we have the scanner instance created by the core code. Pls
note that the CP pre hook can no longer return a RegionScanner and we take that. So this scanner
will be RegionScannerImpl object for sure. That is why the blind assign I did. Make sense?

> 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
>
>
> 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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