liutongwei created HDFS-16490:
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             Summary: CoordinatedCall to observer namnode will requeue util the 
active namenode logsync success
                 Key: HDFS-16490
                 URL: https://issues.apache.org/jira/browse/HDFS-16490
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: namanode
            Reporter: liutongwei


As observer namenode is serving CoordinatedCall, it will requeue call if server 
stateId smaller than client stateId.  In a heavy read but rare write cluster, 
the client may get a stateId not replicated to journal node.

For example,  when client call FSNamesystem.getBlockLocations and need 
updateAccessTime , active namenode call getEditLog().logTimes() but not 
logSync(). Then client get a stateId which do not replicated to journal node. 
So observer name will requeue the client call when nothing trigger a logSync(). 
In rare write cluster, this elapsed time could be from seconds to minutes.

For fix this, we could add a  requeue call timeout  config or return client 
stateId with active committed txid.



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