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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-7368) MetricStore makes cpu spin at 100%
Date Tue, 05 Sep 2017 19:37:02 GMT

    [ https://issues.apache.org/jira/browse/FLINK-7368?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16154170#comment-16154170

ASF GitHub Bot commented on FLINK-7368:

Github user zentol commented on the issue:

    I do see the benefit of a more fine-grained synchronization. What I dislike about using
plain ConcurrentHashMaps everywhere is that accesses to the metrics 99% of the time are done
in batches, and I don't really want to pay the synchronization cost every time.
    That said, the whole "you have to synchronize manually" is a rather big source of bugs
so we may just have to bite the bullet.

> MetricStore makes cpu spin at 100%
> ----------------------------------
>                 Key: FLINK-7368
>                 URL: https://issues.apache.org/jira/browse/FLINK-7368
>             Project: Flink
>          Issue Type: Bug
>          Components: Metrics
>            Reporter: Nico Chen
>            Priority: Blocker
>             Fix For: 1.4.0, 1.3.3
>         Attachments: jm-jstack.log, MyHashMapInfiniteLoopTest.java, MyHashMap.java
> Flink's `MetricStore` is not thread-safe. multi-treads may acess java' hashmap inside
`MetricStore` and can tirgger hashmap's infinte loop. 
> Recently I met the case that flink jobmanager consumed 100% cpu. A part of stacktrace
is shown below. The full jstack is in the attachment.
> {code:java}
> "ForkJoinPool-1-worker-19" daemon prio=10 tid=0x00007fbdacac9800 nid=0x64c1 runnable
>    java.lang.Thread.State: RUNNABLE
>         at java.util.HashMap.put(HashMap.java:494)
>         at org.apache.flink.runtime.webmonitor.metrics.MetricStore.addMetric(MetricStore.java:176)
>         at org.apache.flink.runtime.webmonitor.metrics.MetricStore.add(MetricStore.java:121)
>         at org.apache.flink.runtime.webmonitor.metrics.MetricFetcher.addMetrics(MetricFetcher.java:198)
>         at org.apache.flink.runtime.webmonitor.metrics.MetricFetcher.access$500(MetricFetcher.java:58)
>         at org.apache.flink.runtime.webmonitor.metrics.MetricFetcher$4.onSuccess(MetricFetcher.java:188)
>         at akka.dispatch.OnSuccess.internal(Future.scala:212)
>         at akka.dispatch.japi$CallbackBridge.apply(Future.scala:175)
>         at akka.dispatch.japi$CallbackBridge.apply(Future.scala:172)
>         at scala.PartialFunction$class.applyOrElse(PartialFunction.scala:123)
>         at scala.runtime.AbstractPartialFunction.applyOrElse(AbstractPartialFunction.scala:28)
>         at scala.concurrent.Future$$anonfun$onSuccess$1.apply(Future.scala:117)
>         at scala.concurrent.Future$$anonfun$onSuccess$1.apply(Future.scala:115)
>         at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:32)
>         at java.util.concurrent.ForkJoinTask$AdaptedRunnable.exec(ForkJoinTask.java:1265)
>         at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:334)
>         at java.util.concurrent.ForkJoinWorkerThread.execTask(ForkJoinWorkerThread.java:604)
>         at java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:784)
>         at java.util.concurrent.ForkJoinPool.work(ForkJoinPool.java:646)
>         at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:398)
> {code}
> There are 24 threads show same stacktrace as above to indicate they are spining at HashMap.put(HashMap.java:494)
(I am using Java 1.7.0_6). Many posts indicate multi-threads accessing hashmap cause this
problem and I reproduce the case as well. The test code is attached. I only modify the HashMap.transfer()
by adding concurrent barriers for different treads in order to simulate the timing of creation
of cycles in hashmap's Entry.  My program's stacktrace shows it hangs at same line of HashMap(HashMap.put(HashMap.java:494))
as the stacktrace I post above.
>  Even through `MetricFetcher` has a 10 seconds minimum inteverl between each metrics
qurey, it still cannot guarntee query responses do not acess `MtricStore`'s hashmap concurrently.
 Thus I think it's a bug to fix.

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