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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1172) Blocks in newly completed files are considered under-replicated too quickly
Date Wed, 02 Nov 2011 17:25:33 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1172?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13142319#comment-13142319
] 

Todd Lipcon commented on HDFS-1172:
-----------------------------------

I went back and looked at my branch where I was working on this patch. The remaining work
is to add a test which catches the issue you pointed out with == vs .equals. Since the tests
were passing even with that glaring mistake, the coverage definitely wasn't good enough. I
started to write one and I think I ran into some more issues, but I can't recall what they
were. Since this issue has been around forever, I haven't been able to prioritize it above
other 0.23 work. Is this causing big issues on your clusters that would suggest it should
be prioritized higher?
                
> Blocks in newly completed files are considered under-replicated too quickly
> ---------------------------------------------------------------------------
>
>                 Key: HDFS-1172
>                 URL: https://issues.apache.org/jira/browse/HDFS-1172
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>    Affects Versions: 0.21.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: 0.24.0
>
>         Attachments: HDFS-1172.patch, hdfs-1172.txt, replicateBlocksFUC.patch, replicateBlocksFUC1.patch,
replicateBlocksFUC1.patch
>
>
> I've seen this for a long time, and imagine it's a known issue, but couldn't find an
existing JIRA. It often happens that we see the NN schedule replication on the last block
of files very quickly after they're completed, before the other DNs in the pipeline have a
chance to report the new block. This results in a lot of extra replication work on the cluster,
as we replicate the block and then end up with multiple excess replicas which are very quickly
deleted.

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