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https://issues.apache.org/jira/browse/HDFS-9668?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15623810#comment-15623810
]
Xiao Chen commented on HDFS-9668:
---------------------------------
Thanks [~jingcheng...@intel.com] for working on this. I'm trying to catch up on
this, and hope [~eddyxu] and others could provide their valuable feedback.
Some quick comments/questions on patch 20.
- Why {{AutoCloeableLock#isLocked}} is changed from package private to
protected? Didn't find the use case.
- {{FSDatasetImpl}}: maybe the 300 ms lockWarningThresholdMs can be
configurable?
- {{FSDatasetImpl}}: do we need to keep {{acquireDatasetLock}} in
{{FsDatasetImpl}}?
Since we're changing the internals to have RWlocks, I feel keeping the old
{{acquireDatasetLock}} which calls the write lock is error-prone (perhaps we
should throw {{UnsupportedOperationException}}? not feeling strongly about
this) . Callers should know whether they need a read lock or write lock. I see
some callers are changed (e.g. {{DiskBalancer}}), but some are not (e.g.
{{DataNode}}). At least we should update existing callers accordingly.
- Sorry if I missed some conversations, but it seems [~cmccabe] suggested some
improvements about reducing the lock scope in the earlier comments
([here|https://issues.apache.org/jira/browse/HDFS-9668?focusedCommentId=15193595&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15193595]
and
[here|https://issues.apache.org/jira/browse/HDFS-9668?focusedCommentId=15195782&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15195782]).
Would this be covered here, or is there a separate jira tracking it?
Thanks.
> Optimize the locking in FsDatasetImpl
> -------------------------------------
>
> Key: HDFS-9668
> URL: https://issues.apache.org/jira/browse/HDFS-9668
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Reporter: Jingcheng Du
> Assignee: Jingcheng Du
> Attachments: HDFS-9668-1.patch, HDFS-9668-10.patch,
> HDFS-9668-11.patch, HDFS-9668-12.patch, HDFS-9668-13.patch,
> HDFS-9668-14.patch, HDFS-9668-14.patch, HDFS-9668-15.patch,
> HDFS-9668-16.patch, HDFS-9668-17.patch, HDFS-9668-18.patch,
> HDFS-9668-19.patch, HDFS-9668-19.patch, HDFS-9668-2.patch,
> HDFS-9668-20.patch, HDFS-9668-3.patch, HDFS-9668-4.patch, HDFS-9668-5.patch,
> HDFS-9668-6.patch, HDFS-9668-7.patch, HDFS-9668-8.patch, HDFS-9668-9.patch,
> execution_time.png
>
>
> During the HBase test on a tiered storage of HDFS (WAL is stored in
> SSD/RAMDISK, and all other files are stored in HDD), we observe many
> long-time BLOCKED threads on FsDatasetImpl in DataNode. The following is part
> of the jstack result:
> {noformat}
> "DataXceiver for client DFSClient_NONMAPREDUCE_-1626037897_1 at
> /192.168.50.16:48521 [Receiving block
> BP-1042877462-192.168.50.13-1446173170517:blk_1073779272_40852]" - Thread
> t@93336
> java.lang.Thread.State: BLOCKED
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.createRbw(FsDatasetImpl.java:1111)
> - waiting to lock <18324c9> (a
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl) owned by
> "DataXceiver for client DFSClient_NONMAPREDUCE_-1626037897_1 at
> /192.168.50.16:48520 [Receiving block
> BP-1042877462-192.168.50.13-1446173170517:blk_1073779271_40851]" t@93335
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.createRbw(FsDatasetImpl.java:113)
> at
> org.apache.hadoop.hdfs.server.datanode.BlockReceiver.<init>(BlockReceiver.java:183)
> at
> org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:615)
> 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:745)
> Locked ownable synchronizers:
> - None
>
> "DataXceiver for client DFSClient_NONMAPREDUCE_-1626037897_1 at
> /192.168.50.16:48520 [Receiving block
> BP-1042877462-192.168.50.13-1446173170517:blk_1073779271_40851]" - Thread
> t@93335
> java.lang.Thread.State: RUNNABLE
> at java.io.UnixFileSystem.createFileExclusively(Native Method)
> at java.io.File.createNewFile(File.java:1012)
> at
> org.apache.hadoop.hdfs.server.datanode.DatanodeUtil.createTmpFile(DatanodeUtil.java:66)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.BlockPoolSlice.createRbwFile(BlockPoolSlice.java:271)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.createRbwFile(FsVolumeImpl.java:286)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.createRbw(FsDatasetImpl.java:1140)
> - locked <18324c9> (a
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.createRbw(FsDatasetImpl.java:113)
> at
> org.apache.hadoop.hdfs.server.datanode.BlockReceiver.<init>(BlockReceiver.java:183)
> at
> org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:615)
> 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:745)
> Locked ownable synchronizers:
> - None
> {noformat}
> We measured the execution of some operations in FsDatasetImpl during the
> test. Here following is the result.
> !execution_time.png!
> The operations of finalizeBlock, addBlock and createRbw on HDD in a heavy
> load take a really long time.
> It means one slow operation of finalizeBlock, addBlock and createRbw in a
> slow storage can block all the other same operations in the same DataNode,
> especially in HBase when many wal/flusher/compactor are configured.
> We need a finer grained lock mechanism in a new FsDatasetImpl implementation
> and users can choose the implementation by configuring
> "dfs.datanode.fsdataset.factory" in DataNode.
> We can implement the lock by either storage level or block-level.
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