[jira] Commented: (HDFS-630) In DFSOutputStream.nextBlockOutputStream(), the client can exclude specific datanodes when locating the next block.

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    [ https://issues.apache.org/jira/browse/HDFS-630?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12776791#action_12776791 ] 

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

Cosmin:  I applied your patch but it seems to bring on an issue where I get "java.io.IOException: Cannot complete block: block has not been COMMITTED by the client" closing a log file. See the hdfs-user mailing list.  Grep for message subject: "Cannot complete block: block has not been COMMITTED by the client".  Do you see this?  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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