[CASSANDRA-3253] inherent deadlock situation in commitLog flush?

• Type: Bug
• Status: Resolved
• Priority: Urgent
• Resolution: Fixed
• Fix Version/s: 1.0.0
• Labels: commitlog
• Severity: Critical
• Assignee: Jonathan Ellis
• Reporter: Yang Yang

Authors

Jonathan Ellis

Reviewers

Sylvain Lebresne

• Created: 23/Sep/11 17:53
• Updated: 16/Apr/19 09:32
• Resolved: 26/Sep/11 09:07

Description

after my system ran for a while, it consitently goes into frozen state where all the mutations stage threads are waiting
on the switchlock,

the reason is that the switchlock is held by commit log, as shown by the following thread dump:

"COMMIT-LOG-WRITER" prio=10 tid=0x00000000010df000 nid=0x32d3 waiting on condition [0x00007f2d81557000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)

• parking to wait for <0x00007f3579eec060> (a java.util.concurrent.FutureTask$Sync)
  at java.util.concurrent.locks.LockSupport.park(LockSupport.java:186)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:838)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:998)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1304)
  at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:248)
  at java.util.concurrent.FutureTask.get(FutureTask.java:111)
  at org.apache.cassandra.db.commitlog.CommitLog.getContext(CommitLog.java:386)
  at org.apache.cassandra.db.ColumnFamilyStore.maybeSwitchMemtable(ColumnFamilyStore.java:650)
  at org.apache.cassandra.db.ColumnFamilyStore.forceFlush(ColumnFamilyStore.java:722)
  at org.apache.cassandra.db.commitlog.CommitLog.createNewSegment(CommitLog.java:573)
  at org.apache.cassandra.db.commitlog.CommitLog.access$300(CommitLog.java:81)
  at org.apache.cassandra.db.commitlog.CommitLog$LogRecordAdder.run(CommitLog.java:596)
  at org.apache.cassandra.db.commitlog.PeriodicCommitLogExecutorService$1.runMayThrow(PeriodicCommitLogExecutorService.java:49)
  at org.apache.cassandra.utils.WrappedRunnable.run(WrappedRunnable.java:30)
  at java.lang.Thread.run(Thread.java:679)

we can clearly see that the COMMIT-LOG-WRITER thread is running the regular appender , but the appender itself calls getContext(), which again submits a new Callable to be executed, and waits on the Callable. but the new Callable is never going to be executed since the executor has only one thread.

I believe this is a deterministic bug.