Konstantin Shvachko created HDFS-15915:
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             Summary: Race condition with async edits logging due to updating 
txId outside of the namesystem log
                 Key: HDFS-15915
                 URL: https://issues.apache.org/jira/browse/HDFS-15915
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: hdfs, namenode
            Reporter: Konstantin Shvachko


{{FSEditLogAsync}} creates an {{FSEditLogOp}} and populates its fields inside 
{{FSNamesystem.writeLock}}. But one essential field the transaction id of the 
edits op remains unset until the time when the operation is scheduled for 
synching. At that time {{beginTransaction()}} will set the the 
{{FSEditLogOp.txid}} and increment the global transaction count. On busy 
NameNode this event can fall outside the write lock. 
This causes problems for Observer reads. It also can potentially reshuffle 
transactions and Standby will apply them in a wrong order.



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