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https://issues.apache.org/jira/browse/HDFS-6325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13988209#comment-13988209
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Konstantin Shvachko commented on HDFS-6325:
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An easy way to reproduce this is to create a file on a cluster, then restart NN
without DNs, manually leave SafeMode, and try to append data to the file. On a
real cluster one can kill 3 DNs (on different racks), then some blocks will be
missing, and it is likely that one of them will be the last of some file.
> Append should fail if the last block has unsufficient number of replicas
> ------------------------------------------------------------------------
>
> Key: HDFS-6325
> URL: https://issues.apache.org/jira/browse/HDFS-6325
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 2.2.0
> Reporter: Konstantin Shvachko
>
> Currently append() succeeds on a file with the last block that has no
> replicas. But the subsequent updatePipeline() fails as there are no replicas
> with the exception "Unable to retrieve blocks locations for last block". This
> leaves the file unclosed, and others can not do anything with it until its
> lease expires.
> The solution is to check replicas of the last block on the NameNode and fail
> during append() rather than during updatePipeline().
> How many replicas should be present before NN allows to append? I see two
> options:
> # min-replication: allow append if the last block is minimally replicated (1
> by default)
> # full-replication: allow append if the last block is fully replicated (3 by
> default)
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