Misha Dmitriev created HADOOP-14960:
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Summary: 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
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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