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From "Varun Sharma (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8285) HBaseClient never recovers for single HTable.get() calls when regions move
Date Mon, 08 Apr 2013 07:17:17 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8285?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13625205#comment-13625205
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Varun Sharma commented on HBASE-8285:
-------------------------------------

Thanks for bringing this up ram.

But we run with retries=1 and the retry logic is left to the caller. I guess that is why this
was undetected for so long - with retries=1, everything else works but stuff going through
ServerCallable does not. I guess its still worth fixing this for retries == 1 since connect(tries
!= 0) never executes in such a scenario ?

What do you think ?
                
> HBaseClient never recovers for single HTable.get() calls when regions move
> --------------------------------------------------------------------------
>
>                 Key: HBASE-8285
>                 URL: https://issues.apache.org/jira/browse/HBASE-8285
>             Project: HBase
>          Issue Type: Bug
>          Components: Client
>    Affects Versions: 0.94.6.1
>            Reporter: Varun Sharma
>            Assignee: Varun Sharma
>            Priority: Critical
>             Fix For: 0.98.0, 0.94.7, 0.95.1
>
>         Attachments: 8285-0.94.txt, 8285-trunk.txt
>
>
> Steps to reproduce this bug:
> 1) Gracefull restart a region server causing regions to get redistributed.
> 2) Client call to this region keeps failing since Meta Cache is never purged on the client
for the region that moved.
> Reason behind the bug:
> 1) Client continues to hit the old region server.
> 2) The old region server throws NotServingRegionException which is not handled correctly
and the META cache entries are never purged for that server causing the client to keep hitting
the old server.
> The reason lies in ServerCallable code since we only purge META cache entries when there
is a RetriesExhaustedException, SocketTimeoutException or ConnectException. However, there
is no case check for NotServingRegionException(s).
> Why is this not a problem for Scan(s) and Put(s) ?
> a) If a region server is not hosting a region/scanner, then an UnknownScannerException
is thrown which causes a relocateRegion() call causing a refresh of the META cache for that
particular region.
> b) For put(s), the processBatchCallback() interface in HConnectionManager is used which
clears out META cache entries for all kinds of exceptions except DoNotRetryException.

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