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From "nkeywal (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5877) When a query fails because the region has moved, let the regionserver return the new address to the client
Date Thu, 26 Apr 2012 08:26:13 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5877?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13262462#comment-13262462
] 

nkeywal commented on HBASE-5877:
--------------------------------

bq. Can we mark the failure and make this RegionMovedException behave the same as NotServingRegionException
?
Done.

bq. For updateCachedLocations(), please put explanation for parameter on the same line as
the parameter:
Done.

bq. 'Failed all' -> 'Failed call'
It's an existing comment that we can find again later in the code. It really means "failed
all": all the queries on this server failed. I don't mind changing it to something better,
but I think we should keep the "all".

bq. 'which the server' -> 'which the region'
Done.

bq. Please increase the VERSION of HRegionInterface
Done.

bq. How is the server removed from cache since I see 'continue' above ?
That's what makes this code complex and difficult to change: the error is actually managed
later, when we don't have the real exception anymore.

bq. For ServerManager.sendRegionClose(), please add javadoc for destServerName param.
Done.

bq. Is it possible that destServerName is null ?
Safety checks added.

bq. Please change the above to debug log. && Why is the above fatal (regionResult
!= null) ? Step 4 appears in a comment below the above code. Should the above say step 3 ?
Bad logs fixed.
                
> When a query fails because the region has moved, let the regionserver return the new
address to the client
> ----------------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-5877
>                 URL: https://issues.apache.org/jira/browse/HBASE-5877
>             Project: HBase
>          Issue Type: Improvement
>          Components: client, master, regionserver
>    Affects Versions: 0.96.0
>            Reporter: nkeywal
>            Assignee: nkeywal
>            Priority: Minor
>             Fix For: 0.96.0
>
>         Attachments: 5877.v1.patch
>
>
> This is mainly useful when we do a rolling restart. This will decrease the load on the
master and the network load.
> Note that a region is not immediately opened after a close. So:
> - it seems preferable to wait before retrying on the other server. An optimisation would
be to have an heuristic depending on when the region was closed.
> - during a rolling restart, the server moves the regions then stops. So we may have failures
when the server is stopped, and this patch won't help.
> The implementation in the first patch does:
> - on the region move, there is an added parameter on the regionserver#close to say where
we are sending the region
> - the regionserver keeps a list of what was moved. Each entry is kept 100 seconds.
> - the regionserver sends a specific exception when it receives a query on a moved region.
This exception contains the new address.
> - the client analyses the exeptions and update its cache accordingly...

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