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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1444) Block allocation method does not check pendingCreates for duplicate block ids
Date Fri, 08 Jun 2007 20:15:26 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-1444?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

dhruba borthakur updated HADOOP-1444:

    Attachment: duplicateBlockId2.patch

Implemented all review comments except the one related to "better logging by abandonBlock".
The reason i did not change it in this patch because it is not directly related to this issue
and could conflict with another patch that I have outstanding.  I am going to fix this logging
issue as part of a separate JIRA issue.

> Block allocation method does not check pendingCreates for duplicate block ids
> -----------------------------------------------------------------------------
>                 Key: HADOOP-1444
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1444
>             Project: Hadoop
>          Issue Type: Bug
>          Components: dfs
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: duplicateBlockId2.patch
> The HDFS namenode allocates a new random blockid when requested. It then checks the blocksMap
to verify if this blockid is already in use. If this block is is already in use, it generates
another random number and above process continues. When a blocksid that does not exist in
the blocksMap is found, it stores this blocksid in pendingCreateBlocks and returns the blocksid
to the requesting client.
> The above check for detecting duplicate blockid should check pendingCreateBlocks as well.
> A related problem exists when a file is deleted. Deleting a file causes all its blocks
to be deleted from the blocksMap immediately. These blockids move to recentInvalidateSets
and are sent out to the corresponding datanodes as part of responses to succeeding heartbeats.
So, there is a time window when a block exists in the datanode but not in the blocksMap. At
this time, if the blockid-random-number generator generates a blockid that exists in the datanode
but not on the blocksMap, then the namenode will fail to detect that this is a duplicate blockid.

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