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From Aaron Eng <a...@mapr.com>
Subject Re: Physical memory (bytes) snapshot counter question - how to get maximum memory used in reduce task
Date Thu, 06 Apr 2017 01:37:13 GMT
An important consideration is the difference between the RSS of the JVM process vs. the used
heap size.  Which of those are you looking for? And also, importantly, why/what do you plan
to do with that info?

A second important consideration is the length of time you are at/around your max RSS/java
heap.  Holding X MB of memory for 100ms is very different from holding X MB of memory for
100 seconds.  Are you looking for that info? And if so, how do you plan to use it?

> On Apr 5, 2017, at 6:15 PM, Nico Pappagianis <nico.pappagianis@salesforce.com>
> Hi all
> I've made some memory optimizations on the reduce task and I would like to compare the
old reducer vs new reducer in terms of maximum memory consumption.
> I have a question regarding the description of the following counter:
> PHYSICAL_MEMORY_BYTES | Physical memory (bytes) snapshot | Total physical memory used
by all tasks including spilled data.
> I'm assuming this means the aggregate of memory used throughout the entire reduce task
(if viewing at the reduce task-level). 
> Please correct me if I'm wrong on this assumption (the description seems pretty straightforward).
> Is there a way to get the maximum (not total) memory used by a reduce task from the default
> Thanks!

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