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From "John Zhuge (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7060) Avoid taking locks when sending heartbeats from the DataNode
Date Tue, 29 Mar 2016 04:41:25 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7060?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15215413#comment-15215413
] 

John Zhuge commented on HDFS-7060:
----------------------------------

If we assume dataset lock protects {{bpSlices}}. The following functions access {{bpSlices}}
but they and their callers do NOT lock dataset. Did I miss anything? Is this a bug?
{code}
FsVolumeImpl#addBlockPool   (this is a write access to bpSlices)
  FsVolumeImpl#addBlockPool
    FsDatasetImpl#addVolume

FsVolumeImpl#getBlockPoolUsed
  FsVolumeList#getBlockPoolUsed
    FsDatasetImpl#getBlockPoolUsed

FsVolumeImpl#getBlockPoolSlice
  (too many callers, hard to track down !)

FsVolumeImpl#getBlockPoolList
  DirectoryScanner.ReportCompiler#call

FsVolumeImpl#checkDirs
  FsVolumeImpl#checkDirs
    FsDatasetImpl#checkDataDir

...
{code}

A few suggestions regarding lock usage:
* All locks including intrinsic locks should include docs that clearly state what resources
they protect.
* Locks should be used in the classes they are defined. Very hard to reason if their usages
are scattered around.

If we want to protect {{bpSlices}} with lock, can we just use {{bpSlices}} intrinsic lock
instead of dataset lock?


> Avoid taking locks when sending heartbeats from the DataNode
> ------------------------------------------------------------
>
>                 Key: HDFS-7060
>                 URL: https://issues.apache.org/jira/browse/HDFS-7060
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Haohui Mai
>            Assignee: Xinwei Qin 
>              Labels: BB2015-05-TBR
>         Attachments: HDFS-7060-002.patch, HDFS-7060.000.patch, HDFS-7060.001.patch
>
>
> We're seeing the heartbeat is blocked by the monitor of {{FsDatasetImpl}} when the DN
is under heavy load of writes:
> {noformat}
>    java.lang.Thread.State: BLOCKED (on object monitor)
>         at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.getDfsUsed(FsVolumeImpl.java:115)
>         - waiting to lock <0x0000000780304fb8> (a org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl)
>         at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.getStorageReports(FsDatasetImpl.java:91)
>         - locked <0x0000000780612fd8> (a java.lang.Object)
>         at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.sendHeartBeat(BPServiceActor.java:563)
>         at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.offerService(BPServiceActor.java:668)
>         at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:827)
>         at java.lang.Thread.run(Thread.java:744)
>    java.lang.Thread.State: BLOCKED (on object monitor)
>         at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.createRbw(FsDatasetImpl.java:743)
>         - waiting to lock <0x0000000780304fb8> (a org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl)
>         at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.createRbw(FsDatasetImpl.java:60)
>         at org.apache.hadoop.hdfs.server.datanode.BlockReceiver.<init>(BlockReceiver.java:169)
>         at org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:621)
>         at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opWriteBlock(Receiver.java:124)
>         at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:71)
>         at org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:232)
>         at java.lang.Thread.run(Thread.java:744)
>    java.lang.Thread.State: RUNNABLE
>         at java.io.UnixFileSystem.createFileExclusively(Native Method)
>         at java.io.File.createNewFile(File.java:1006)
>         at org.apache.hadoop.hdfs.server.datanode.DatanodeUtil.createTmpFile(DatanodeUtil.java:59)
>         at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.BlockPoolSlice.createRbwFile(BlockPoolSlice.java:244)
>         at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.createRbwFile(FsVolumeImpl.java:195)
>         at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.createRbw(FsDatasetImpl.java:753)
>         - locked <0x0000000780304fb8> (a org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl)
>         at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.createRbw(FsDatasetImpl.java:60)
>         at org.apache.hadoop.hdfs.server.datanode.BlockReceiver.<init>(BlockReceiver.java:169)
>         at org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:621)
>         at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opWriteBlock(Receiver.java:124)
>         at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:71)
>         at org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:232)
>         at java.lang.Thread.run(Thread.java:744)
> {noformat}



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