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https://issues.apache.org/jira/browse/LUCENE-1990?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Toke Eskildsen updated LUCENE-1990:
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Attachment: performance-te20100226.txt
LUCENE-1990-te20100226b.patch
I couldn't help making a tiny tweak to the performance test so that it outputs
execution time means for the different implementations. I have attached
measurements from 5 different 64 bit machines. Looking at the means, I observe
the following:
* i7 Q820 and Xeon L5420: Practically no difference between aligned and
packed with a small edge to aligned
* Core 2 and Xeon 5148: Aligned is consistently about 10% slower than packed
* Xeon MP (old with just 1 MB CPU cache): Aligned ranges from 0-10% slower
than packed, depending on bits/value
The direct implementations outperforms packed and aligned for all sane cases
(using direct8 to hold only 1 bit/value is clearly a bad idea). No surprise
there.
Caveat: The tests were run without any other significantly resource heavy
processes disturbing it. This means that there were no fighting for the CPU
cache.
Major caveat: Tests are needed on other processors than 64 bit Intel.
I would be great if someone could figure out how to make an aligned getter
without using division as that is surely the thing that hampers aligned
performance.
> Add unsigned packed int impls in oal.util
> -----------------------------------------
>
> Key: LUCENE-1990
> URL: https://issues.apache.org/jira/browse/LUCENE-1990
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Michael McCandless
> Priority: Minor
> Attachments: LUCENE-1990-te20100122.patch,
> LUCENE-1990-te20100210.patch, LUCENE-1990-te20100212.patch,
> LUCENE-1990-te20100223.patch, LUCENE-1990-te20100226.patch,
> LUCENE-1990-te20100226b.patch, LUCENE-1990.patch,
> LUCENE-1990_PerformanceMeasurements20100104.zip, performance-te20100226.txt
>
>
> There are various places in Lucene that could take advantage of an
> efficient packed unsigned int/long impl. EG the terms dict index in
> the standard codec in LUCENE-1458 could subsantially reduce it's RAM
> usage. FieldCache.StringIndex could as well. And I think "load into
> RAM" codecs like the one in TestExternalCodecs could use this too.
> I'm picturing something very basic like:
> {code}
> interface PackedUnsignedLongs {
> long get(long index);
> void set(long index, long value);
> }
> {code}
> Plus maybe an iterator for getting and maybe also for setting. If it
> helps, most of the usages of this inside Lucene will be "write once"
> so eg the set could make that an assumption/requirement.
> And a factory somewhere:
> {code}
> PackedUnsignedLongs create(int count, long maxValue);
> {code}
> I think we should simply autogen the code (we can start from the
> autogen code in LUCENE-1410), or, if there is an good existing impl
> that has a compatible license that'd be great.
> I don't have time near-term to do this... so if anyone has the itch,
> please jump!
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