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From "Hemanth Yamijala (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2815) Allowing processes to cleanup dfs on shutdown
Date Mon, 03 Mar 2008 06:10:50 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2815?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12574351#action_12574351
] 

Hemanth Yamijala commented on HADOOP-2815:
------------------------------------------

While Devaraj and I were trying to fix HADOOP-2899, we came up with a solution that exactly
matches Dhruba's comment above. In HADOOP-2899, JobTracker needed to cleanup the directory
pointed to by mapred.system.dir when it is shutting down. We experimented with some code in
the JobTracker that adds a shutdown hook and deletes the directory at cleanup. The requirement
for deleting the directory works, but we faced the following problems:
- the addition / removal of additional shutdown hooks sometimes causes IllegalStateExceptions
in the FileSystem code
- the non-deterministic order of running shutdown hooks in the JVM actually makes the whole
thing complicated, and seemed unsafe.

Dhruba's solution would work perfectly to handle this scenario, and seems a very clean approach.
The JobTracker would just register a shutdown hook with the FileSystem, and would cleanup
the system directory then. So, +1 for the suggestion.

Is there any chance this code can come up in Hadoop 0.16.1 because HADOOP-2899 should ideally
be fixed in 0.16.1 ?


> Allowing processes to cleanup dfs on shutdown
> ---------------------------------------------
>
>                 Key: HADOOP-2815
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2815
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs
>            Reporter: Olga Natkovich
>            Assignee: dhruba borthakur
>
> Pig creates temp files that it wants to be removed at the end of the processing. The
code that removes the temp file is in the shutdown hook so that they get removed both under
normal shutdown as well as when process gets killed.
> The problem that we are seeing is that by the time the code is called the DFS might already
be closed and the delete fails leaving temp files behind. Since we have no control over the
shutdown order, we have no way to make sure that the files get removed.
> One way to solve this issue is to be able to mark the files as temp files so that hadoop
can remove them during its shutdown.
> The stack trace I am seeing is
> at org.apache.hadoop.dfs.DFSClient.checkOpen(DFSClient.java:158)
>         at org.apache.hadoop.dfs.DFSClient.delete(DFSClient.java:417)
>         at org.apache.hadoop.dfs.DistributedFileSystem.delete(DistributedFileSystem.java:144)
>         at org.apache.pig.backend.hadoop.datastorage.HPath.delete(HPath.java:96)
>         at org.apache.pig.impl.io.FileLocalizer$1.run(FileLocalizer.java:275)

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