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https://issues.apache.org/jira/browse/CASSANDRA-12689?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15513841#comment-15513841
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Benjamin Roth commented on CASSANDRA-12689:
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As a graph this may look like this: https://cl.ly/0N3l0D1v1P1H
You can see the mutations increase linearly. The drop was always after having
restarted C*.
This is just an example, this scenarios happened much more often.
This is the load graph of the same time window: https://cl.ly/2m1S2K081o3n
> All MutationStage threads blocked, kills server
> -----------------------------------------------
>
> Key: CASSANDRA-12689
> URL: https://issues.apache.org/jira/browse/CASSANDRA-12689
> Project: Cassandra
> Issue Type: Bug
> Components: Local Write-Read Paths
> Reporter: Benjamin Roth
> Priority: Critical
>
> Under heavy load (e.g. due to repair during normal operations), a lot of
> NullPointerExceptions occur in MutationStage. Unfortunately, the log is not
> very chatty, trace is missing:
> 2016-09-22T06:29:47+00:00 cas6 [MutationStage-1]
> org.apache.cassandra.concurrent.AbstractLocalAwareExecutorService Uncaught
> exception on thread Thread[MutationStage-1,5,main]: {}
> 2016-09-22T06:29:47+00:00 cas6 #011java.lang.NullPointerException: null
> Then, after some time, in most cases ALL threads in MutationStage pools are
> completely blocked. This leads to piling up pending tasks until server runs
> OOM and is completely unresponsive due to GC. Threads will NEVER unblock
> until server restart. Even if load goes completely down, all hints are
> paused, and no compaction or repair is running. Only restart helps.
> I can understand that pending tasks in MutationStage may pile up under heavy
> load, but tasks should be processed and dequeud after load goes down. This is
> definitively not the case. This looks more like a an unhandled exception
> leading to a stuck lock.
> Stack trace from jconsole, all Threads in MutationStage show same trace.
> Name: MutationStage-48
> State: WAITING on java.util.concurrent.CompletableFuture$Signaller@fcc8266
> Total blocked: 137 Total waited: 138.513
> Stack trace:
> sun.misc.Unsafe.park(Native Method)
> java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
> java.util.concurrent.CompletableFuture$Signaller.block(CompletableFuture.java:1693)
> java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3323)
> java.util.concurrent.CompletableFuture.waitingGet(CompletableFuture.java:1729)
> java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1895)
> com.google.common.util.concurrent.Uninterruptibles.getUninterruptibly(Uninterruptibles.java:137)
> org.apache.cassandra.db.Mutation.apply(Mutation.java:227)
> org.apache.cassandra.db.Mutation.apply(Mutation.java:241)
> org.apache.cassandra.hints.Hint.apply(Hint.java:96)
> org.apache.cassandra.hints.HintVerbHandler.doVerb(HintVerbHandler.java:91)
> org.apache.cassandra.net.MessageDeliveryTask.run(MessageDeliveryTask.java:66)
> java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
> org.apache.cassandra.concurrent.AbstractLocalAwareExecutorService$FutureTask.run(AbstractLocalAwareExecutorService.java:162)
> org.apache.cassandra.concurrent.AbstractLocalAwareExecutorService$LocalSessionFutureTask.run(AbstractLocalAwareExecutorService.java:134)
> org.apache.cassandra.concurrent.SEPWorker.run(SEPWorker.java:109)
> java.lang.Thread.run(Thread.java:745)
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