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https://issues.apache.org/jira/browse/HBASE-25905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17450506#comment-17450506
 ] 

Duo Zhang commented on HBASE-25905:
-----------------------------------

OK, I think I found a possible way to reproduce this.

We need to schedule two sync requests, and the reason for the first sync is 
that we have reached the batch size. So after the first sync request fails, we 
will add all the entries in unackedAppends back to toWriteAppends, which makes 
the size of all the entries in the unackedAppends greater than the batch size. 
So next when we start to write again, we can not write all the entries in the 
unackedAppends at once, then we will face the problem described above by 
[~Xiaolin Ha].

Let me prepare a UT first. Thanks [~Xiaolin Ha] for the great digging!

> Shutdown of WAL stuck at waitForSafePoint
> -----------------------------------------
>
>                 Key: HBASE-25905
>                 URL: https://issues.apache.org/jira/browse/HBASE-25905
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver, wal
>    Affects Versions: 3.0.0-alpha-1, 2.0.0
>            Reporter: Xiaolin Ha
>            Assignee: Xiaolin Ha
>            Priority: Critical
>         Attachments: rs-jstack1, rs-jstack2, wal-stuck-error-logs.png
>
>
> We use the fan-out HDFS OutputStream and AsyncFSWAL on our clusters, but met 
> the problem than RS can not exit completely for several hours util manual 
> interventions.
> The two jstacks below show that the regionserver thread can waiting 
> unlimitedly in both 
> AsyncFSWAL#waitForSafePoint()
> {code:java}
> "regionserver/gh-data-hbase-finance08.mt/10.22.179.24:16020" #29 prio=5 
> os_prio=0 tid=0x00007fb2feb5c000 nid=0xa92b waiting on condition 
> [0x00007f9ccb992000]
>    java.lang.Thread.State: WAITING (parking)
>         at sun.misc.Unsafe.park(Native Method)
>         - parking to wait for  <0x00007faea229a9d0> (a 
> java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
>         at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
>         at 
> java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitUninterruptibly(AbstractQueuedSynchronizer.java:1976)
>         at 
> org.apache.hadoop.hbase.regionserver.wal.AsyncFSWAL.waitForSafePoint(AsyncFSWAL.java:687)
>         at 
> org.apache.hadoop.hbase.regionserver.wal.AsyncFSWAL.doShutdown(AsyncFSWAL.java:743)
>         at 
> org.apache.hadoop.hbase.regionserver.wal.AbstractFSWAL.shutdown(AbstractFSWAL.java:900)
>         at 
> org.apache.hadoop.hbase.wal.AbstractFSWALProvider.shutdown(AbstractFSWALProvider.java:182)
>         at 
> org.apache.hadoop.hbase.wal.RegionGroupingProvider.shutdown(RegionGroupingProvider.java:232)
>         at 
> org.apache.hadoop.hbase.wal.WALFactory.shutdown(WALFactory.java:271)
>         at 
> org.apache.hadoop.hbase.regionserver.HRegionServer.shutdownWAL(HRegionServer.java:1405)
>         at 
> org.apache.hadoop.hbase.regionserver.HRegionServer.run(HRegionServer.java:1147)
>         at java.lang.Thread.run(Thread.java:745)
> {code}
> and the log roller stuck at waiting for lock
> {code:java}
> "regionserver/gh-data-hbase-finance08.mt/10.22.179.24:16020.logRoller" #322 
> daemon prio=5 os_prio=0 tid=0x00007fb2e11a4000 nid=0xa953 waiting on 
> condition [0x00007f9cbd9f1000]
>    java.lang.Thread.State: WAITING (parking)
>         at sun.misc.Unsafe.park(Native Method)
>         - parking to wait for  <0x00007faea1217048> (a 
> java.util.concurrent.locks.ReentrantLock$FairSync)
>         at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
>         at 
> java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
>         at 
> java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
>         at 
> java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
>         at 
> java.util.concurrent.locks.ReentrantLock$FairSync.lock(ReentrantLock.java:224)
>         at 
> java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
>         at 
> org.apache.hadoop.hbase.regionserver.wal.AbstractFSWAL.rollWriter(AbstractFSWAL.java:822)
>         at 
> org.apache.hadoop.hbase.wal.AbstractWALRoller$RollController.rollWal(AbstractWALRoller.java:269)
>         at 
> org.apache.hadoop.hbase.wal.AbstractWALRoller.run(AbstractWALRoller.java:186){code}
>  



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