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https://issues.apache.org/jira/browse/HDFS-16785?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17615141#comment-17615141
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ASF GitHub Bot commented on HDFS-16785:
---------------------------------------
ZanderXu commented on PR #4945:
URL: https://github.com/apache/hadoop/pull/4945#issuecomment-1273427206
```
final FsVolumeImpl fsVolume =
createFsVolume(sd.getStorageUuid(), sd, location);
// no need to add lock
final ReplicaMap tempVolumeMap = new ReplicaMap();
ArrayList<IOException> exceptions = Lists.newArrayList();
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);
}
}
```
The `fsVolume` here is a local temporary variable and still not be added
into the `volumes`, and add/remove bp operations just use the volume in
`volumes`, so there is no conflicts. So here doesn't need the lock for
`BlockPoolSlice`.
@Hexiaoqiao Sir, can check it again?
> 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
> Priority: Major
> Labels: pull-request-available
>
> 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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