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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3294) distcp leaves empty blocks afte successful execution
Date Tue, 22 Apr 2008 16:43:21 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3294?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12591358#action_12591358
] 

Doug Cutting commented on HADOOP-3294:
--------------------------------------

Verifying lengths is cheap and would catch many problems.  It could be done by the reducer,
and the output could list any discrepancies.  Checking CRC's is more expensive and should
be optional if implemented.

> Verifying file sizes could have some implication when we support "appends".

That's true, so we shouldn't have a discrepancy fail the job, but it should still be logged
so that the user can see which files were modified after they were copied.

> distcp leaves empty blocks afte successful execution
> ----------------------------------------------------
>
>                 Key: HADOOP-3294
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3294
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: util
>    Affects Versions: 0.16.3
>         Environment: 0.16.3 without any patches. Dfs permissions turned off everywhere,
such that HADOOP-3138 and HADOOP-3186 do not apply
>            Reporter: Christian Kunz
>
> I copied around 40 TB between two hadoop clusters, with distcp running on source.
> Job was *successful*, but one destination file was empty because of its only block being
empty.
> None of the distcp log files have any mentioning of this file.
> There were a couple of messages in the namenode server log of the destination cluster
referencing the file:
> hadoop-xxxnamenode-yyy.log.2008-04-19:2008-04-19 02:19:15,666 INFO org.apache.hadoop.dfs.StateChange:
BLOCK* NameSystem.allocateBlock: destinationDir/_distcp_tmp_z0g93p/fileName. blk_-9209890281741927376
> hadoop-xxx-namenode-yyy.log.2008-04-19:2008-04-19 02:54:45,820 WARN org.apache.hadoop.dfs.StateChange:
DIR* NameSystem.internalReleaseCreate: attempt to release a create lock on destinationDir/_distcp_tmp_z0g93p/fileName
file does not exist.
> distcp should not rely on the user to double-check.
> Would it make sense to add a reducer  to compare destination file sizes with source files
sizes and do some appropriate action?

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