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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Assigned: (HDFS-350) DFSClient more robust if the namenode is busy doing GC
Date Wed, 29 Sep 2010 18:45:35 GMT

     [ https://issues.apache.org/jira/browse/HDFS-350?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

dhruba borthakur reassigned HDFS-350:

    Assignee: dhruba borthakur

> DFSClient more robust if the namenode is busy doing GC
> ------------------------------------------------------
>                 Key: HDFS-350
>                 URL: https://issues.apache.org/jira/browse/HDFS-350
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
> In the current code, if the client (writer) encounters an RPC error while fetching a
new block id from the namenode, it does not retry. It throws an exception to the application.
This becomes especially bad if the namenode is in the middle of a GC and does not respond
in time. The reason the client throws an exception is because it does not know whether the
namenode successfully allocated a block for this file.
> One possible enhancement would be to make the client retry the addBlock RPC if needed.
The client can send the block list that it currently has. The namenode can match the block
list send by the client with what it has in its own metadata and then send back a new blockid
(or a previously allocated blockid that the client had not yet received because the earlier
RPC timedout). This will make the client more robust!
> This works even when we support Appends because the namenode will *always* verify that
the client has the lease for the file in question.

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