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https://issues.apache.org/jira/browse/HDFS-8496?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15229144#comment-15229144
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Wei-Chiu Chuang commented on HDFS-8496:
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Link HDFS-10267, which founds/fixes a bug in HDFS-8496.
> Calling stopWriter() with FSDatasetImpl lock held may block other threads
> -------------------------------------------------------------------------
>
> Key: HDFS-8496
> URL: https://issues.apache.org/jira/browse/HDFS-8496
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 2.6.0
> Reporter: zhouyingchao
> Assignee: Colin Patrick McCabe
> Fix For: 2.8.0
>
> Attachments: HDFS-8496-001.patch, HDFS-8496.002.patch,
> HDFS-8496.003.patch, HDFS-8496.004.patch
>
>
> On a DN of a HDFS 2.6 cluster, we noticed some DataXceiver threads and
> heartbeat threads are blocked for quite a while on the FSDatasetImpl lock. By
> looking at the stack, we found the calling of stopWriter() with FSDatasetImpl
> lock blocked everything.
> Following is the heartbeat stack, as an example, to show how threads are
> blocked by FSDatasetImpl lock:
> {code}
> java.lang.Thread.State: BLOCKED (on object monitor)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.getDfsUsed(FsVolumeImpl.java:152)
> - waiting to lock <0x00000007701badc0> (a
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.getAvailable(FsVolumeImpl.java:191)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.getStorageReports(FsDatasetImpl.java:144)
> - locked <0x0000000770465dc0> (a java.lang.Object)
> at
> org.apache.hadoop.hdfs.server.datanode.BPServiceActor.sendHeartBeat(BPServiceActor.java:575)
> at
> org.apache.hadoop.hdfs.server.datanode.BPServiceActor.offerService(BPServiceActor.java:680)
> at
> org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:850)
> at java.lang.Thread.run(Thread.java:662)
> {code}
> The thread which held the FSDatasetImpl lock is just sleeping to wait another
> thread to exit in stopWriter(). The stack is:
> {code}
> java.lang.Thread.State: TIMED_WAITING (on object monitor)
> at java.lang.Object.wait(Native Method)
> at java.lang.Thread.join(Thread.java:1194)
> - locked <0x00000007636953b8> (a org.apache.hadoop.util.Daemon)
> at
> org.apache.hadoop.hdfs.server.datanode.ReplicaInPipeline.stopWriter(ReplicaInPipeline.java:183)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.recoverCheck(FsDatasetImpl.java:982)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.recoverClose(FsDatasetImpl.java:1026)
> - locked <0x00000007701badc0> (a
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl)
> at
> org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:624)
> at
> org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opWriteBlock(Receiver.java:137)
> at
> org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:74)
> at
> org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:235)
> at java.lang.Thread.run(Thread.java:662)
> {code}
> In this case, we deployed quite a lot other workloads on the DN, the local
> file system and disk is quite busy. We guess this is why the stopWriter took
> quite a long time.
> Any way, it is not quite reasonable to call stopWriter with the FSDatasetImpl
> lock held. In HDFS-7999, the createTemporary() is changed to call
> stopWriter without FSDatasetImpl lock. We guess we should do so in the other
> three methods: recoverClose()/recoverAppend/recoverRbw().
> I'll try to finish a patch for this today.
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