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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-630) In DFSOutputStream.nextBlockOutputStream(), the client can exclude specific datanodes when locating the next block.
Date Sat, 14 Nov 2009 23:54:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-630?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12778021#action_12778021
] 

stack commented on HDFS-630:
----------------------------

I've been playing running loadings against a small hbase cluster of 4 nodes -- a usual hbase
initial setup -- with and without this patch on the hadoop 0.21 branch.  With this patch in
place, the loading completes though I kill a regionserver and DN.  Without it, the loading
fails because more than one regionserver dies complaining that it can't allocate a block to
write a flush file (NN keeps giving it the dead DN as the home for new block and never moves
on).

+1 on this patch.

Cosmin, mind making a version for TRUNK as per Dhruba's suggestion?  Thanks.

> In DFSOutputStream.nextBlockOutputStream(), the client can exclude specific datanodes
when locating the next block.
> -------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-630
>                 URL: https://issues.apache.org/jira/browse/HDFS-630
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: hdfs client
>    Affects Versions: 0.21.0
>            Reporter: Ruyue Ma
>            Assignee: Ruyue Ma
>            Priority: Minor
>             Fix For: 0.21.0
>
>         Attachments: 0001-Fix-HDFS-630-for-0.21.patch, HDFS-630.patch
>
>
> created from hdfs-200.
> If during a write, the dfsclient sees that a block replica location for a newly allocated
block is not-connectable, it re-requests the NN to get a fresh set of replica locations of
the block. It tries this dfs.client.block.write.retries times (default 3), sleeping 6 seconds
between each retry ( see DFSClient.nextBlockOutputStream).
> This setting works well when you have a reasonable size cluster; if u have few datanodes
in the cluster, every retry maybe pick the dead-datanode and the above logic bails out.
> Our solution: when getting block location from namenode, we give nn the excluded datanodes.
The list of dead datanodes is only for one block allocation.

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