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https://issues.apache.org/jira/browse/HADOOP-4663?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12661732#action_12661732
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Konstantin Shvachko commented on HADOOP-4663:
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> In fact, the blocks here are not temporary any more.

This is the key. They are not temporary so why do we keep them in tmp 
directory? Why DNs cannot report them to the name-node? It is just a matter of 
reporting the right length, right?

> disable "sync" on 0.18.3, will be an API incompatiblity from 0.18.2.

This is not incompatibility. The feature does not work correctly in 0.18.2 and 
it will still not work correctly in 0.18.3 with the advantage of not causing 
all the problems.
I think removing everything under tmp as Raghu proposes is the right solution 
for 0.18.3.
We should talk about the "real" fix in terms of 0.19 and up. This seems to be a 
consensus among colleagues around me.

> 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: 0.18.3
>
>         Attachments: deleteTmp.patch, deleteTmp2.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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