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From "Wei-Chiu Chuang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8496) Calling stopWriter() with FSDatasetImpl lock held may block other threads
Date Wed, 06 Apr 2016 21:22:25 GMT

    [ 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:
---------------------------------------

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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