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From "He Yongqiang (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-2841) Task level native optimization
Date Fri, 03 Feb 2012 02:33:54 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2841?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13199485#comment-13199485

He Yongqiang commented on MAPREDUCE-2841:

Really cool stuff! 
In terms of CPU performance, can you also do some comparison with new java output collector
that Todd mentioned (https://github.com/facebook/hadoop-20/blob/master/src/mapred/org/apache/hadoop/mapred/BlockMapOutputBuffer.java)?
In facebook's internal tests, we have seen a big improvement(8x-10x) for cpu spent in sort
(e.g., example 1: 
240M->30M, example 2: 9M->1.8M), and total mapper CPU of 2x ( example 1: 707M ->
440M, example 2: 40M->19M). They are CPU numbers, not latency numbers. BlockMapOutputBuffer.java
uses only one thread but the original collector uses 2 threads. But the latency is still improved
by a lot (like 30%). 

with some analysis on performance differences, it will really help understand some bottlenecks
and the difference that language brings.

> Task level native optimization
> ------------------------------
>                 Key: MAPREDUCE-2841
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2841
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: task
>         Environment: x86-64 Linux
>            Reporter: Binglin Chang
>            Assignee: Binglin Chang
>         Attachments: DESIGN.html, MAPREDUCE-2841.v1.patch, MAPREDUCE-2841.v2.patch, dualpivot-0.patch,
> I'm recently working on native optimization for MapTask based on JNI. 
> The basic idea is that, add a NativeMapOutputCollector to handle k/v pairs emitted by
mapper, therefore sort, spill, IFile serialization can all be done in native code, preliminary
test(on Xeon E5410, jdk6u24) showed promising results:
> 1. Sort is about 3x-10x as fast as java(only binary string compare is supported)
> 2. IFile serialization speed is about 3x of java, about 500MB/s, if hardware CRC32C is
used, things can get much faster(1G/s).
> 3. Merge code is not completed yet, so the test use enough io.sort.mb to prevent mid-spill
> This leads to a total speed up of 2x~3x for the whole MapTask, if IdentityMapper(mapper
does nothing) is used.
> There are limitations of course, currently only Text and BytesWritable is supported,
and I have not think through many things right now, such as how to support map side combine.
I had some discussion with somebody familiar with hive, it seems that these limitations won't
be much problem for Hive to benefit from those optimizations, at least. Advices or discussions
about improving compatibility are most welcome:) 
> Currently NativeMapOutputCollector has a static method called canEnable(), which checks
if key/value type, comparator type, combiner are all compatible, then MapTask can choose to
enable NativeMapOutputCollector.
> This is only a preliminary test, more work need to be done. I expect better final results,
and I believe similar optimization can be adopt to reduce task and shuffle too. 

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