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https://issues.apache.org/jira/browse/HADOOP-1444?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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dhruba borthakur updated HADOOP-1444:
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Status: Patch Available (was: Open)
> 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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