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https://issues.apache.org/jira/browse/HADOOP-4663?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12665356#action_12665356
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dhruba borthakur commented on HADOOP-4663:
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In the "append world" (i.e 0.19), the semantics that we provide is that data
written by a writer may be seen by other readers even if the writer has not
invoked "sync". HDFS makes every effort (within reasonable cost limits) to
persist data that is written to a file. Moreover, the "append" protocol uses
the generation stamp of the block to accurately determine stale blocks, thus it
is safe to promote blocks from the "blocksBeingWritten" directory to the real
block directory.
The data corruption you have seen occured because the
generation-stamp-update-procotol is not triggered during a block transfer
request. This patch correctly handles block-trasfer-requests and should prevent
the data corruption issue from occuring.
> Datanode should delete files under tmp when upgraded from 0.17
> --------------------------------------------------------------
>
> Key: HADOOP-4663
> URL: https://issues.apache.org/jira/browse/HADOOP-4663
> Project: Hadoop Core
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.18.0
> Reporter: Raghu Angadi
> Assignee: dhruba borthakur
> Priority: Blocker
> Fix For: 0.19.1
>
> Attachments: deleteTmp.patch, deleteTmp2.patch, deleteTmp_0.18.patch,
> handleTmp1.patch
>
>
> Before 0.18, when Datanode restarts, it deletes files under data-dir/tmp
> directory since these files are not valid anymore. But in 0.18 it moves these
> files to normal directory incorrectly making them valid blocks. One of the
> following would work :
> - remove the tmp files during upgrade, or
> - if the files under /tmp are in pre-18 format (i.e. no generation), delete
> them.
> Currently effect of this bug is that, these files end up failing block
> verification and eventually get deleted. But cause incorrect over-replication
> at the namenode before that.
> Also it looks like our policy regd treating files under tmp needs to be
> defined better. Right now there are probably one or two more bugs with it.
> Dhruba, please file them if you rememeber.
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