[jira] [Created] (HDFS-5454) DataNode UUID should be assigned prior to FsDataset initialization

["Eric Sirianni (JIRA)" <ji...@apache.org>]

Eric Sirianni created HDFS-5454:
-----------------------------------

             Summary: DataNode UUID should be assigned prior to FsDataset initialization
                 Key: HDFS-5454
                 URL: https://issues.apache.org/jira/browse/HDFS-5454
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: datanode
    Affects Versions: 2.2.0
            Reporter: Eric Sirianni
            Assignee: Arpit Agarwal
            Priority: Minor


The DataNode's UUID ({{DataStorage.getDatanodeUuid()}} field) is NULL at the point where the {{FsDataset}} object is created ({{DataNode.initStorage()}}.  

As the {{DataStorage}} object is an input to the {{FsDataset}} factory method, it is desirable for it to be fully populated with a UUID at this point.  In particular, our {{FsDatasetSpi}} implementation relies upon the DataNode UUID as a key to access our underlying block storage device.

This also appears to be a regression compared to Hadoop 1.x - our 1.x {{FSDatasetInterface}} plugin has a non-NULL UUID on startup.  I haven't fully traced through the code, but I suspect this came from the {{BPOfferService}}/{{BPServiceActor}} refactoring to support federated namenodes.

With HDFS-5448, the DataNode is now responsible for generating its own UUID.  This greatly simplifies the fix.  Move the UUID check/generation in from {{DataNode.createBPRegistration()}} to {{DataNode.initStorage()}}.  This more naturally co-locates UUID generation immediately subsequent to the read of the UUID from the {{DataStorage}} properties file.

{code}
  private void initStorage(final NamespaceInfo nsInfo) throws IOException {
    // ...

      final String bpid = nsInfo.getBlockPoolID();
      //read storage info, lock data dirs and transition fs state if necessary
      storage.recoverTransitionRead(this, bpid, nsInfo, dataDirs, startOpt);
      
      // SUGGESTED NEW PLACE TO CHECK DATANODE UUID
      checkDatanodeUuid();

    // ...
  }
{code}



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