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From 易剑 <myhad...@gmail.com>
Subject Re: [jira] Updated: (MAPREDUCE-64) Map-side sort is hampered by io.sort.record.percent
Date Mon, 28 Dec 2009 04:41:30 GMT
2009/12/23 Chris Douglas (JIRA) <jira@apache.org>

>
>     [
> https://issues.apache.org/jira/browse/MAPREDUCE-64?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel]
>
> Chris Douglas updated MAPREDUCE-64:
> -----------------------------------
>
>    Status: Open  (was: Patch Available)
>
> > Map-side sort is hampered by io.sort.record.percent
> > ---------------------------------------------------
> >
> >                 Key: MAPREDUCE-64
> >                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-64
> >             Project: Hadoop Map/Reduce
> >          Issue Type: Bug
> >            Reporter: Arun C Murthy
> >            Assignee: Chris Douglas
> >         Attachments: M64-0.patch, M64-0i.png, M64-1.patch, M64-1i.png,
> M64-2.patch, M64-2i.png, M64-3.patch, M64-4.patch, M64-5.patch
> >
> >
> > Currently io.sort.record.percent is a fairly obscure, per-job
> configurable, expert-level parameter which controls how much accounting
> space is available for records in the map-side sort buffer (io.sort.mb).
> Typically values for io.sort.mb (100) and io.sort.record.percent (0.05)
> imply that we can store ~350,000 records in the buffer before necessitating
> a sort/combine/spill.
> > However for many applications which deal with small records e.g. the
> world-famous wordcount and it's family this implies we can only use 5-10% of
> io.sort.mb i.e. (5-10M) before we spill inspite of having _much_ more memory
> available in the sort-buffer. The word-count for e.g. results in ~12 spills
> (given hdfs block size of 64M). The presence of a combiner exacerbates the
> problem by piling serialization/deserialization of records too...
> > Sure, jobs can configure io.sort.record.percent, but it's tedious and
> obscure; we really can do better by getting the framework to automagically
> pick it by using all available memory (upto io.sort.mb) for either the data
> or accounting.
>
> --
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>
>


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