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From "Duo Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-19047) CP exposed Scanner types should not extend Shipper
Date Thu, 26 Oct 2017 06:35:00 GMT

    [ 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:
-----------------------------------

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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