[jira] Commented: (HADOOP-4663) Datanode should delete files under tmp when upgraded from 0.17

["Raghu Angadi (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-4663?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12661673#action_12661673 ] 

Raghu Angadi commented on HADOOP-4663:
--------------------------------------

A few comments :

-  since only the blocks that were part of writes could be valid, it it better to create them in "tmp_valid" or "tmp_writes" directory?
- The rest of the blocks in tmp will be deleted automatically. This fixes the rebalancer issue as well. We can not leave any possible corruptions.

- It is very crucial that any files left over should not cause corruption that we have already seen. 
    -- Simpler and better alternative for 0.18.3 might be to just say sync() is not supported and remove everything under tmp (same as 0.17).
    -- This way it gives more time this jira to make sure there are no cases where it could cause corruption. 

- The patch move all the files to top level directory. But datanode data directories are organized to limit each directory to 64 blocks and 64 subdirectories. The current policy violates that. Overtime datanodes could end up having very large number of files in top level directory.
   -- But this is not very important to fix in 0.18.. but it should be fixed in 0.19 or another line. A seperate jira might help.

> 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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