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https://issues.apache.org/jira/browse/HBASE-19047?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16222823#comment-16222823
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Appy commented on HBASE-19047:
------------------------------
Given the core design is already out there, and not a part of this patch, you
don't necessarily have to change it. This patch is already changing things for
good. So am all +1 for it. Which path do you want, take your pick:
- Deleting the check and assign and get it in for alpha4.
- Separate out shipper from RegionScanner.
- Change RegionScanner *is a* Shipper (inheritance) to RegionScanner *has a*
Shipper (composition). And if the scanner after postScannerOpen returns empty
Optional, then go with a default shipper. (Probably best to do in follow-on for
beta1)
{noformat}
RegionScanner implements ShipperProvider {...}
interface ShipperProvider {
Optional<Shipper> getShipper();
}
{noformat}
> 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
> Priority: Critical
> Fix For: 2.0.0-alpha-4
>
> Attachments: HBASE-19047.patch, HBASE-19047_V2.patch,
> HBASE-19047_V2.patch, HBASE-19047_V3.patch, HBASE-19047_V4.patch,
> HBASE-19047_V4.patch, HBASE-19047_V4.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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