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From "Todd Lipcon (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-2970) Contending block synchronizations can result in scary log messages
Date Fri, 17 Feb 2012 20:56:57 GMT
Contending block synchronizations can result in scary log messages
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                 Key: HDFS-2970
                 URL: https://issues.apache.org/jira/browse/HDFS-2970
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: data-node
    Affects Versions: 0.23.0
            Reporter: Todd Lipcon


If multiple datanodes are attempting to act as the coordinator for a block recovery, but one
is being particularly slow, it's possible that you see the following interleaving:
- Primary A receives block recovery command for recovery genstamp = 1, then starts acting
slow
- Primary B receives block recovery command for recovery genstamp = 2
- Primary B calls initReplicaRecovery on other nodes for genstamp = 2
- Primary A calls initReplicaRecovery on other nodes for genstamp = 1
This results in a scary message. For example:

java.io.IOException: java.io.IOException: THIS IS NOT SUPPOSED TO HAPPEN: replica.getGenerationStamp()
>= recoveryId = 4148, block=blk_6899379920748342698_4136, replica=FinalizedReplica, blk_6899379920748342698_4176,
FINALIZED

BUT, this scenario is properly handled by the recovery protocol. We should tone down the message
a bit.

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