[jira] [Created] (HDFS-16785) DataNode hold BP write lock to scan disk

["ZanderXu (Jira)" <ji...@apache.org>]

ZanderXu created HDFS-16785:
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             Summary: DataNode hold BP write lock to scan disk
                 Key: HDFS-16785
                 URL: https://issues.apache.org/jira/browse/HDFS-16785
             Project: Hadoop HDFS
          Issue Type: Improvement
            Reporter: ZanderXu
            Assignee: ZanderXu


When patching the fine-grained locking of datanode, I  found that `addVolume` will hold the write block of the BP lock to scan the new volume to get the blocks. If we try to add one full volume that was fixed offline before, i will hold the write lock for a long time.

The related code as bellows:
{code:java}
for (final NamespaceInfo nsInfo : nsInfos) {
  String bpid = nsInfo.getBlockPoolID();
  try (AutoCloseDataSetLock l = lockManager.writeLock(LockLevel.BLOCK_POOl, bpid)) {
    fsVolume.addBlockPool(bpid, this.conf, this.timer);
    fsVolume.getVolumeMap(bpid, tempVolumeMap, ramDiskReplicaTracker);
  } catch (IOException e) {
    LOG.warn("Caught exception when adding " + fsVolume +
        ". Will throw later.", e);
    exceptions.add(e);
  }
} {code}
And I noticed that this lock is added by HDFS-15382, means that this logic is not in lock before. 



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