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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-9618) Add thread which detects JVM pauses
Date Thu, 06 Jun 2013 16:41:21 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9618?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13677214#comment-13677214
] 

Todd Lipcon commented on HADOOP-9618:
-------------------------------------

Hey Hitesh. We already have the "EventCounter" log4j appender. Rather than making one-off
metrics for this, I think we should just extend the EventCounter to take a list of regular
expressions to map to metrics in the logs - eg you could say something the following in the
log4j configuration:

{code}
log4j.appender.EventCounter.WARN.gc-pauses=Detected pause in JVM
{code}

Does that seem like a more general way of achieving the above?

bq. FWIW, -XX:UseGCLogFileRotation is available in JDK 6u34 and 7u2+.
Thanks, I forgot about that new feature. Still it's nicer to have this info exposed via log4j,
and with a consistent format (the Java GC logs keep changing format and also look different
depending on which collector you're using, if I recall correctly)
                
> 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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