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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-1444) Block allocation method does not check pendingCreates for duplicate block ids
Date Wed, 30 May 2007 17:30:15 GMT
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

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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