[HDFS-16785] Avoid to hold write lock to improve performance when add volume.

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.4.0
• Fix Version/s: 3.4.0
• Component/s: datanode
• Labels: pull-request-available
• Target Version/s: 3.4.0
• Hadoop Flags: Reviewed
• Assignee: ZanderXu
• Reporter: ZanderXu
• Created: 28/Sep/22 09:19
• Updated: 28/Jan/24 08:02
• Resolved: 13/Nov/22 14:05

Description

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:

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);
  }
} 

And I noticed that this lock is added by HDFS-15382, means that this logic is not in lock before. 

Issue Links

• relates to: HDFS-15382 Split one FsDatasetImpl lock to volume grain locks.
• links to: GitHub Pull Request #4945