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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1172) Blocks in newly completed files are considered under-replicated too quickly
Date Mon, 21 Mar 2011 21:42:06 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1172?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13009404#comment-13009404
] 

Hairong Kuang commented on HDFS-1172:
-------------------------------------

A block under construction keeps track of the pipeline. So NN knows the block's pipeline length,
which is represented by r1+r2 in above algorithm.

> 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
>         Attachments: HDFS-1172.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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