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Date: Wed, 2 May 2012 15:58:51 +0000 (UTC)
From: "nkeywal (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (HBASE-5877) When a query fails because the
 region has moved, let the regionserver return the new address to the client
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    [ https://issues.apache.org/jira/browse/HBASE-5877?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13266656#comment-13266656 ] 

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

Generated with protobuf 2.4.1

Here are the things I'm not a big fan, but for which I don't have a better solution:
- the move management in the client code: I think it's possible to change the way we manage error (don't wait for all results before retrying), but that would be for another JIRA
- the destination is the closeRegion interface is a kind of interface hijacking. Other options would be:
    - sharing the region state in zookeeper
    - letting the regionserver calls the master to get the new server. On paper this would be more efficient than a client -> master call. In both cases we could consider that the client should not connect to the master except for cluster administration (create table, split regin; ...). That would increase global reliability. That's for another discussion as well I think.

Here is what I plan to do in the final version
- move the handler functional code into a function in HRegionServer: this would allow to have the function addToMovedRegion as private instead of public.
- Change all the CloseRegionHandler to take a RegionServer instead of a server? I'm not really keen on adding a class RegionServerServices, but may be I should?
- Manage the case when the destination is not specified at the beginning of the move (may be in a different Jira if it's not simple)...

All the previous comment should have been taken into account.
                
> 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, 5877.v6.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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