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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 Tue, 01 Jun 2010 14:34:43 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1172?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12874030#action_12874030
] 

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

> Primary DN send the blockReceived on account of all DNs.
This will cause race condition: primary DN reports that block B is received at DN1 but after
that NN receives a block report from DN1 that it does not have B.

One option is that checkReplicationFactor(newFile) put the block in PendingReplicationBlocks
queue instead of neededReplication queue since NN knows exactly from whom it is expecting
blockReceived.

> 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
>
> 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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