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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-7368) MetricStore makes cpu spin at 100%
Date Thu, 10 Aug 2017 03:51:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-7368?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16121011#comment-16121011

ASF GitHub Bot commented on FLINK-7368:

Github user asdf2014 commented on a diff in the pull request:

    --- Diff: flink-runtime-web/src/main/java/org/apache/flink/runtime/webmonitor/metrics/MetricStore.java
    @@ -24,8 +24,8 @@
     import org.slf4j.Logger;
     import org.slf4j.LoggerFactory;
    -import java.util.HashMap;
    -import java.util.HashSet;
    +import java.util.concurrent.ConcurrentHashMap;
    +import java.util.concurrent.ConcurrentSkipListSet;
    --- End diff --
    Hi, @nicochen . Thank you for the `PR`. There is a import order problem, you should change
the order of those import as the following code. Otherwise it will not pass the `checkstyle`
    import java.util.Map;
    import java.util.Set;
    import java.util.concurrent.ConcurrentHashMap;
    import java.util.concurrent.ConcurrentSkipListSet;

> 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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