[jira] [Created] (HDFS-14126) DataNode DirectoryScanner holding global lock for too long

["Wei-Chiu Chuang (JIRA)" <ji...@apache.org>]

Wei-Chiu Chuang created HDFS-14126:
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             Summary: DataNode DirectoryScanner holding global lock for too long
                 Key: HDFS-14126
                 URL: https://issues.apache.org/jira/browse/HDFS-14126
             Project: Hadoop HDFS
          Issue Type: Bug
    Affects Versions: 3.0.0
            Reporter: Wei-Chiu Chuang


I've got a Hadoop 3 based cluster set up, and this DN has just 434 thousand blocks.

And yet, DirectoryScanner holds the fsdataset lock for 2.7 seconds:

{quote}
2018-12-03 21:33:09,130 INFO org.apache.hadoop.hdfs.server.datanode.DirectoryScanner: BlockPool BP-4588049-10.17.XXX-XX-XXXX281857726 Total blocks: 434401, missing metadata fi
les:0, missing block files:0, missing blocks in memory:0, mismatched blocks:0
2018-12-03 21:33:09,131 WARN org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Lock held time above threshold: lock identifier: org.apache.hadoop.hdfs.serve
r.datanode.fsdataset.impl.FsDatasetImpl lockHeldTimeMs=2710 ms. Suppressed 0 lock warnings. The stack trace is: java.lang.Thread.getStackTrace(Thread.java:1559)
org.apache.hadoop.util.StringUtils.getStackTrace(StringUtils.java:1032)
org.apache.hadoop.util.InstrumentedLock.logWarning(InstrumentedLock.java:148)
org.apache.hadoop.util.InstrumentedLock.check(InstrumentedLock.java:186)
org.apache.hadoop.util.InstrumentedLock.unlock(InstrumentedLock.java:133)
org.apache.hadoop.util.AutoCloseableLock.release(AutoCloseableLock.java:84)
org.apache.hadoop.util.AutoCloseableLock.close(AutoCloseableLock.java:96)
org.apache.hadoop.hdfs.server.datanode.DirectoryScanner.scan(DirectoryScanner.java:473)
org.apache.hadoop.hdfs.server.datanode.DirectoryScanner.reconcile(DirectoryScanner.java:373)
org.apache.hadoop.hdfs.server.datanode.DirectoryScanner.run(DirectoryScanner.java:318)
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
java.lang.Thread.run(Thread.java:748)
{quote}

Log messages like this repeats every several hours (6, to be exact). I am not sure if this is a performance regression, or just the fact that the lock information is printed in Hadoop 3. [~vagarychen] or [~templedf] do you know?

There's no log in DN to indicate any sort of JVM GC going on. Plus, the DN's heap size is set to several GB.



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