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https://issues.apache.org/jira/browse/MAPREDUCE-5785?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13925743#comment-13925743
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Gera Shegalov commented on MAPREDUCE-5785:
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[~sandyr], please elaborate regarding increased chances of OOM. Currently, if
the users have not tuned Xmx, they'll get 200m. With the patch, the'll get
770m. If the user specified map reduce.\*.memory.mb smaller than the default
1024 (also minimum-allocation-mb), I don't allow the Xmx be lower than the
previous default Xmx200m in the patch.
Regarding the reversal of which parameter controls the other, I can see it
either way. Your point works for me. But it is also convenient to explicitly
state the cap for the container. The latter seems to be more
backwards-compatible.
> Derive task attempt JVM max heap size automatically from mapreduce.*.memory.mb
> ------------------------------------------------------------------------------
>
> Key: MAPREDUCE-5785
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5785
> Project: Hadoop Map/Reduce
> Issue Type: New Feature
> Components: mr-am, task
> Reporter: Gera Shegalov
> Assignee: Gera Shegalov
> Attachments: MAPREDUCE-5785.v01.patch
>
>
> Currently users have to set 2 memory-related configs per Job / per task type.
> One first chooses some container size map reduce.\*.memory.mb and then a
> corresponding maximum Java heap size Xmx < map reduce.\*.memory.mb. This
> makes sure that the JVM's C-heap (native memory + Java heap) does not exceed
> this mapreduce.*.memory.mb. If one forgets to tune Xmx, MR-AM might be
> - allocating big containers whereas the JVM will only use the default
> -Xmx200m.
> - allocating small containers that will OOM because Xmx is too high.
> With this JIRA, we propose to set Xmx automatically based on an empirical
> ratio that can be adjusted. Xmx is not changed automatically if provided by
> the user.
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