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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-11667) Simplify ClientScanner logic for NSREs.
Date Tue, 05 Aug 2014 01:23:12 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11667?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14085626#comment-14085626
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Devaraj Das commented on HBASE-11667:
-------------------------------------

[~lhofhansl], HBASE-11665 is tracking failures in the TestRegionReplicas. For scan tests you
should run TestReplicasClient tests - that has tests for scans with replicas. Will have a
look at your patch.

> Simplify ClientScanner logic for NSREs.
> ---------------------------------------
>
>                 Key: HBASE-11667
>                 URL: https://issues.apache.org/jira/browse/HBASE-11667
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>             Fix For: 0.99.0, 0.98.5, 2.0.0, 0.94.23
>
>         Attachments: 11667-0.94.txt, 11667-trunk.txt
>
>
> We ran into an issue with Phoenix where a RegionObserver coprocessor intercepts a scan
and returns an aggregate (in this case a count) with a fake row key. It turns out this does
not work when the {{ClientScanner}} encounters NSREs, as it uses the last key it saw to reset
the scanner to try again (which in this case would be the fake key).
> While this is arguably a rare case and one could also argue that a region observer just
shouldn't do this... While looking at {{ClientScanner}}'s code I found this logic not necessary.
> A NSRE occurred because we contacted a region server with a key that it no longer hosts.
This is the start key, so it is always correct to retry with this same key. That simplifies
the ClientScanner logic and also make this sort of coprocessors possible,



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