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https://issues.apache.org/jira/browse/HADOOP-14960?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16261861#comment-16261861
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Misha Dmitriev commented on HADOOP-14960:
-----------------------------------------
[~xkrogen] indeed, the GC time percentage is likely to go up and down all the
time. Do you mean this code at line 190 in JvmMetrics.java, correct?
{code}
if (gcTimeMonitor != null) {
rb.addCounter(GcTimePercentage,
gcTimeMonitor.getLatestGcData().getGcTimePercentage());
}
{code}
Replacing {{addCounter}} with {{addGauge}} is trivial. [~xiaochen] how (in
which ticket) would you recommend to submit a patch for this change?
> Add GC time percentage monitor/alerter
> --------------------------------------
>
> Key: HADOOP-14960
> URL: https://issues.apache.org/jira/browse/HADOOP-14960
> Project: Hadoop Common
> Issue Type: Improvement
> Reporter: Misha Dmitriev
> Assignee: Misha Dmitriev
> Fix For: 3.0.0, 2.10.0
>
> Attachments: HADOOP-14960.01.patch, HADOOP-14960.02.patch,
> HADOOP-14960.03.patch, HADOOP-14960.04.patch
>
>
> Currently class {{org.apache.hadoop.metrics2.source.JvmMetrics}} provides
> several metrics related to GC. Unfortunately, all these metrics are not as
> useful as they could be, because they don't answer the first and most
> important question related to GC and JVM health: what percentage of time my
> JVM is paused in GC? This percentage, calculated as the sum of the GC pauses
> over some period, like 1 minute, divided by that period - is the most
> convenient measure of the GC health because:
> - it is just one number, and it's clear that, say, 1..5% is good, but 80..90%
> is really bad
> - it allows for easy apple-to-apple comparison between runs, even between
> different apps
> - when this metric reaches some critical value like 70%, it almost always
> indicates a "GC death spiral", from which the app can recover only if it
> drops some task(s) etc.
> The existing "total GC time", "total number of GCs" etc. metrics only give
> numbers that can be used to rougly estimate this percentage. Thus it is
> suggested to add a new metric to this class, and possibly allow users to
> register handlers that will be automatically invoked if this metric reaches
> the specified threshold.
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