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Date: Sat, 20 Jul 2013 15:18:48 +0000 (UTC)
From: "Vinay (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12658893.1374333499591.86052.1374333528929@arcas>
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Subject: [jira] [Created] (HDFS-5014)
 BPOfferService#processCommandFromActor() synchronization on namenode RPC
 call delays IBR to Active NN, if Stanby NN is unstable
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Vinay created HDFS-5014:
---------------------------

             Summary: BPOfferService#processCommandFromActor() synchronization on namenode RPC call delays IBR to Active NN, if Stanby NN is unstable
                 Key: HDFS-5014
                 URL: https://issues.apache.org/jira/browse/HDFS-5014
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: datanode, ha
    Affects Versions: 2.0.4-alpha
            Reporter: Vinay
            Assignee: Vinay


In one of our cluster, following has happened which failed HDFS write.

1. Standby NN was unstable and continously restarting due to some errors. But Active NN was stable.
2. MR Job was writing files.
3. At some point SNN went down again while datanode processing the REGISTER command for SNN. 
4. Datanodes started retrying to connect to SNN to register at the following code  in BPServiceActor#retrieveNamespaceInfo() which will be called under synchronization.
{code}      try {
        nsInfo = bpNamenode.versionRequest();
        LOG.debug(this + " received versionRequest response: " + nsInfo);
        break;{code}
Unfortunately in all datanodes at same point this happened.
5. For next 7-8 min standby was down, and no blocks were reported to active NN at this point and writes have failed.


So culprit is {{BPOfferService#processCommandFromActor()}} is completely synchronized which is not required.

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