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https://issues.apache.org/jira/browse/HDFS-16855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17641740#comment-17641740
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ASF GitHub Bot commented on HDFS-16855:
---------------------------------------
MingXiangLi commented on PR #5170:
URL: https://github.com/apache/hadoop/pull/5170#issuecomment-1333372902
The BLOCK_POOl level lock is to protect replica consistency for
FsDataSetImpl when read or write operating happend at same time.
> forbid refresh() when ReplicaCachingGetSpaceUsed #init() at first time，it
will cause the value of dfsUsage to be 0 until the next time refresh().
For example we can use df command instead at first time or other way.
On my side It's less risky to change ReplicaCachingGetSpaceUsed logic than
remove the write lock.
Or we can further discussion to make sure no case will lead to consistency
problem if we remove write lock.
> Remove the redundant write lock in addBlockPool
> -----------------------------------------------
>
> Key: HDFS-16855
> URL: https://issues.apache.org/jira/browse/HDFS-16855
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: dingshun
> Priority: Major
> Labels: pull-request-available
>
> When patching the datanode's fine-grained lock, we found that the datanode
> couldn't start，maybe happened deadlock，when addBlockPool, so we can remove it.
> {code:java}
> // getspaceused classname
> <property>
> <name>fs.getspaceused.classname</name>
>
> <value>org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.ReplicaCachingGetSpaceUsed</value>
> </property> {code}
> {code:java}
> //
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl#addBlockPool
>
> // get writeLock
> @Override
> public void addBlockPool(String bpid, Configuration conf)
> throws IOException {
> LOG.info("Adding block pool " + bpid);
> AddBlockPoolException volumeExceptions = new AddBlockPoolException();
> try (AutoCloseableLock lock = lockManager.writeLock(LockLevel.BLOCK_POOl,
> bpid)) {
> try {
> volumes.addBlockPool(bpid, conf);
> } catch (AddBlockPoolException e) {
> volumeExceptions.mergeException(e);
> }
> volumeMap.initBlockPool(bpid);
> Set<String> vols = storageMap.keySet();
> for (String v : vols) {
> lockManager.addLock(LockLevel.VOLUME, bpid, v);
> }
> }
>
> } {code}
> {code:java}
> //
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl#deepCopyReplica
> // need readLock
> void replicas(String bpid, Consumer<Iterator<ReplicaInfo>> consumer) {
> LightWeightResizableGSet<Block, ReplicaInfo> m = null;
> try (AutoCloseDataSetLock l = lockManager.readLock(LockLevel.BLOCK_POOl,
> bpid)) {
> m = map.get(bpid);
> if (m !=null) {
> m.getIterator(consumer);
> }
> }
> } {code}
>
> because it is not the same thread, so the write lock cannot be downgraded to
> a read lock
> {code:java}
> void addBlockPool(final String bpid, final Configuration conf) throws
> IOException {
> long totalStartTime = Time.monotonicNow();
> final Map<FsVolumeSpi, IOException> unhealthyDataDirs =
> new ConcurrentHashMap<FsVolumeSpi, IOException>();
> List<Thread> blockPoolAddingThreads = new ArrayList<Thread>();
> for (final FsVolumeImpl v : volumes) {
> Thread t = new Thread() {
> public void run() {
> try (FsVolumeReference ref = v.obtainReference()) {
> FsDatasetImpl.LOG.info("Scanning block pool " + bpid +
> " on volume " + v + "...");
> long startTime = Time.monotonicNow();
> v.addBlockPool(bpid, conf);
> long timeTaken = Time.monotonicNow() - startTime;
> FsDatasetImpl.LOG.info("Time taken to scan block pool " + bpid +
> " on " + v + ": " + timeTaken + "ms");
> } catch (IOException ioe) {
> FsDatasetImpl.LOG.info("Caught exception while scanning " + v +
> ". Will throw later.", ioe);
> unhealthyDataDirs.put(v, ioe);
> }
> }
> };
> blockPoolAddingThreads.add(t);
> t.start();
> }
> for (Thread t : blockPoolAddingThreads) {
> try {
> t.join();
> } catch (InterruptedException ie) {
> throw new IOException(ie);
> }
> }
> } {code}
>
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