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https://issues.apache.org/jira/browse/KYLIN-1034?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14933458#comment-14933458
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Daniel Lemire commented on KYLIN-1034:
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Let me add that using formally immutable bitmaps means that you are less likely
to need to "copy" (through "clone") your bitmaps. Avoiding copies can reduce
the number of cache misses. It also reduces the burden on the garbage
collector, by potentially creating fewer intermediate objects.
I saw a couple of "clone" calls in the code, if these are frequently called,
they could be a source of inefficiency.
To do computations with Roaring bitmaps, you should never need to call "clone".
We have static calls that take immutable bitmaps and generate a new bitmap.
> Faster bitmap indexes with Roaring bitmaps
> ------------------------------------------
>
> Key: KYLIN-1034
> URL: https://issues.apache.org/jira/browse/KYLIN-1034
> Project: Kylin
> Issue Type: Improvement
> Components: General
> Affects Versions: Future
> Reporter: Daniel Lemire
> Labels: performance
> Attachments: roaring-0001.patch
>
>
> Kylin is using ConciseSet for bitmap indexing. It was found that Roaring
> bitmaps are often much better than ConciseSet (e.g., see experimental section
> in http://arxiv.org/pdf/1402.6407.pdf ). The compression is often better and
> the speed difference can be substantial. This is even more so with version
> 0.5 of Roaring.
> There is a high quality Java implementation that is used by Apache Spark and
> Druid.io. The Druid people found that switching to Roaring bitmaps could
> improve real-world performance by 30% or more.
> Source code:
> https://github.com/lemire/RoaringBitmap/
> Importing from Maven:
> http://central.maven.org/maven2/org/roaringbitmap/RoaringBitmap/0.5.3/
> <dependencies>
> <dependency>
> <groupId>org.roaringbitmap</groupId>
> <artifactId>RoaringBitmap</artifactId>
> <version>[0.5,)</version>
> </dependency>
> </dependencies>
> Online API :
> http://lemire.me/docs/RoaringBitmap/
> JavaDoc Jar:
> http://central.maven.org/maven2/org/roaringbitmap/RoaringBitmap/0.5.3/RoaringBitmap-0.5.3-javadoc.jar
> When desired, the library supports memory file mapping, so that out-of-JVM
> heap memory is used instead. This can greatly improve IO issues. The library
> is available under the Apache license and is patent-free.
> There is an extensive real-data benchmark framework which you can run for
> yourself to compare Roaring with competitive alternatives such as ConciseSet :
> https://github.com/lemire/RoaringBitmap/tree/master/jmh
> Running such a benchmark can be as simple as launching a script.
> For Druid, the bitmap format was made "pluggable" so you can switch from one
> format to the other using a configuration flag. This is implemented through
> simple wrappers, e.g., see
> https://github.com/metamx/bytebuffer-collections/tree/master/src/main/java/com/metamx/collections/bitmap
> So it can be really easy to make it possible to switch the format while
> preserving backward compatibility if needed...
> It is probably not difficult work to integrate Roaring in Kylin (maybe a day
> or so of programming) and it could potentially improve performance while
> reducing memory storage.
> Note: Roaring bitmaps were also adopted in Apache Lucene, though they have
> their own implementation, see
> https://www.elastic.co/blog/frame-of-reference-and-roaring-bitmaps
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