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https://issues.apache.org/jira/browse/HDFS-14459?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Stephen O'Donnell updated HDFS-14459:
-------------------------------------
Status: Patch Available (was: Open)
> ClosedChannelException silently ignored in FsVolumeList.addBlockPool()
> ----------------------------------------------------------------------
>
> Key: HDFS-14459
> URL: https://issues.apache.org/jira/browse/HDFS-14459
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Affects Versions: 3.3.0
> Reporter: Stephen O'Donnell
> Assignee: Stephen O'Donnell
> Priority: Major
> Fix For: 3.3.0
>
> Attachments: HDFS-14459.001.patch
>
>
> Following on HDFS-14333, I encountered another scenario when a volume has
> some sort of disk level errors it can silently fail to have the blockpool
> added to itself in FsVolumeList.addBlockPool().
> In the logs for a recent issue we see the following pattern:
> {code}
> 2019-04-24 04:21:27,690 INFO
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Added
> volume - /CDH/sdi1/dfs/dn/current, StorageType: DISK
> 2019-04-24 04:21:27,691 INFO
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Added
> new volume: DS-694ae931-8a4e-42d5-b2b3-d946e35c6b47
> ...
> 2019-04-24 04:21:27,703 INFO
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Scanning
> block pool BP-936404344-xxx-1426594942733 on volume
> /CDH/sdi1/dfs/dn/current...
> ...
> <HERE WE ARE MISSING THE LOG LIKE:
> 2019-04-24 04:21:27,722 INFO
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Time
> taken to scan block pool BP-936404344-xxx-1426594942733 on
> /CDH/sdi1/dfs/dn/current: 19ms
> >
> ...
> 2019-04-24 04:21:29,871 INFO
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Adding
> replicas to map for block pool BP-936404344-xxx-1426594942733 on volume
> /CDH/sdi1/dfs/dn/current...
> ...
> 2019-04-24 04:21:29,872 INFO
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Caught
> exception while adding replicas from /CDH/sdi1/dfs/dn/current. Will throw
> later.
> java.io.IOException: block pool BP-936404344-10.7.192.215-1426594942733 is
> not found
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.getBlockPoolSlice(FsVolumeImpl.java:407)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.getVolumeMap(FsVolumeImpl.java:864)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeList$1.run(FsVolumeList.java:191
> {code}
> The notable point, is that the 'scanning block pool' step must not have
> completed properly for this volume but nothing was logged and then the
> slightly confusing error is logged when attempting to add the replicas. That
> error occurs as the block pool was not added to the volume by the
> addBlockPool step.
> The relevant part of the code in 'addBlockPool()' from current trunk looks
> like:
> {code}
> 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 (ClosedChannelException e) {
> // ignore.
> } catch (IOException ioe) {
> FsDatasetImpl.LOG.info("Caught exception while scanning " + v +
> ". Will throw later.", ioe);
> unhealthyDataDirs.put(v, ioe);
> }
> }
> };
> blockPoolAddingThreads.add(t);
> t.start();
> }
> {code}
> As we get the first log message (Scanning block pool ... ), but not the
> second (Time take to scan block pool ...), and we don't get anything logged
> or an exception thrown, then the operation must have encountered a
> ClosedChannelException which is silently ignored.
> I am also not sure if we should ignore a ClosedChannelException, as it means
> the volume failed to add fully. As ClosedChannelException is a subclass of
> IOException perhaps we can remove that catch block entirely?
> Finally, HDFS-14333 refactored the above code to allow the DN to better
> handle a disk failure on DN startup. However, if addBlockPool does throw an
> exception, it will mean getAllVolumesMap() will not get called and the DN
> will end up partly initialized.
> DataNode.initBlockPool() calls FsDatasetImpl.addBlockPool() which looks like
> the following, calling addBlockPool() and then getAllVolumesMap():
> {code}
> public void addBlockPool(String bpid, Configuration conf)
> throws IOException {
> LOG.info("Adding block pool " + bpid);
> try (AutoCloseableLock lock = datasetLock.acquire()) {
> volumes.addBlockPool(bpid, conf);
> volumeMap.initBlockPool(bpid);
> }
> volumes.getAllVolumesMap(bpid, volumeMap, ramDiskReplicaTracker);
> }
> {code}
> This needs refactored to catch any AddBlockPoolException raised in
> addBlockPool, then continue to call getAllVolumesMap() before re-throwing any
> of the caught exceptions to allow the DN to handle the individual volume
> failures.
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