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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1332) When unable to place replicas, BlockPlacementPolicy should log reasons nodes were excluded
Date Thu, 12 May 2011 20:55:47 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1332?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13032671#comment-13032671
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Tsz Wo (Nicholas), SZE commented on HDFS-1332:
----------------------------------------------

Hi Todd, it is questionable whether this is a nice error message.  Too many error messages
confuse users.

Replication also uses {{BlockPlacementPolicy}}.  Have you counted it?  Also, your example
is just one example.  It may not be a good representative.

Moreover, the performance degradation is twofold:
# it takes time to create the messages/objects, and
# it creates additional objects for GC.

> When unable to place replicas, BlockPlacementPolicy should log reasons nodes were excluded
> ------------------------------------------------------------------------------------------
>
>                 Key: HDFS-1332
>                 URL: https://issues.apache.org/jira/browse/HDFS-1332
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: Todd Lipcon
>            Assignee: Ted Yu
>            Priority: Minor
>              Labels: newbie
>             Fix For: 0.23.0
>
>         Attachments: HDFS-1332.patch
>
>
> Whenever the block placement policy determines that a node is not a "good target" it
could add the reason for exclusion to a list, and then when we log "Not able to place enough
replicas" we could say why each node was refused. This would help new users who are having
issues on pseudo-distributed (eg because their data dir is on /tmp and /tmp is full). Right
now it's very difficult to figure out the issue.

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