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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4663) Datanode should delete files under tmp when upgraded from 0.17
Date Tue, 20 Jan 2009 20:20:59 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4663?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12665542#action_12665542
] 

Konstantin Shvachko commented on HADOOP-4663:
---------------------------------------------

Append or not if we want files be visible by other clients there should be a logic which reads
files in the tmp directory. And this is not related to promoting incomplete files. We do not
have guarantees for the data to survive crashes if it has not been sync-ed even if another
client has seen it.

> the "append" protocol uses the generation stamp to accurately determine stale blocks
> it is safe to promote blocks from the "blocksBeingWritten" directory

If the protocol worked correctly it would be safe to promote any incomplete blocks including
those in blocksBeingReplicated but it wasn't.

I would rather not promote unsynced files because
# it turned to be error-prone
# it adds performance overhead, when sync or append is not used.

> 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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