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https://issues.apache.org/jira/browse/SPARK-2142?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sandy Ryza resolved SPARK-2142.
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Resolution: Not a Problem
I ran some tests that indicated that only stop-the-world GC time gets included
in the GC Time metric.
> Give better indicator of how GC cuts into task time
> ---------------------------------------------------
>
> Key: SPARK-2142
> URL: https://issues.apache.org/jira/browse/SPARK-2142
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core
> Reporter: Sandy Ryza
>
> The currently reported GC time is a somewhat misleading metric.
> If I see a task that has taken 10 minutes with a GC time of 9 minutes, the
> straightforward interpretation is that GC is making my job 90% slower. This
> is true if all that time is spent in a full GC. But if a GC thread is only
> running in the background, it might not be impacting my task at all.
> What a user really wants to know is whether GC is the cause of their task
> being slow. Counting the number of full GCs or measuring the amount of time
> spent in stop-the-world GCs could be a more useful metric.
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