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https://issues.apache.org/jira/browse/HADOOP-9618?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13675436#comment-13675436
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Colin Patrick McCabe commented on HADOOP-9618:
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I kind of wish we could use the JVM's {{Xloggc:logfile}} to get this
information, since theoretically it should be more trustworthy than trying to
guess. Is that too much hassle to configure by default?
I suppose the thread method detects machine pauses which are *not* the result
of GCs, so you could say that it gives more information (although perhaps more
questionable information).
I'm a little gun-shy of the 1 second timeout. It wasn't too long ago that the
Linux scheduler quantum was 100 milliseconds. So if you had ten threads
hogging the CPU, you'd already have no time left to run your watchdog thread.
I think the timeout either needs to be longer, or the thread needs to be a
high-priority thread, possibly even realtime priority.
Have you tried running this with a gnarly MapReduce job going on?
> Add thread which detects JVM pauses
> -----------------------------------
>
> Key: HADOOP-9618
> URL: https://issues.apache.org/jira/browse/HADOOP-9618
> Project: Hadoop Common
> Issue Type: New Feature
> Components: util
> Affects Versions: 3.0.0
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Attachments: hadoop-9618.txt
>
>
> Often times users struggle to understand what happened when a long JVM pause
> (GC or otherwise) causes things to malfunction inside a Hadoop daemon. For
> example, a long GC pause while logging an edit to the QJM may cause the edit
> to timeout, or a long GC pause may make other IPCs to the NameNode timeout.
> We should add a simple thread which loops on 1-second sleeps, and if the
> sleep ever takes significantly longer than 1 second, log a WARN. This will
> make GC pauses obvious in logs.
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