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From "Mark Harwood (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-4069) Segment-level Bloom filters
Date Mon, 13 Aug 2012 10:30:38 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4069?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13433045#comment-13433045
] 

Mark Harwood commented on LUCENE-4069:
--------------------------------------

bq. Removing misleading 2X perf gain: it seems to depend heavily on the exact use case.

Fair enough - the original patch targeted Lucene 3.6 which benefited more heavily from this
technique. The issue then morphed into a 4.x patch where performance gains were harder to
find. 
I think the sweet spot is in primary key searches on indexes with ongoing heavy changes (more
segment fragmentation, less OS-level caching?). This is the use case I am targeting currently
and my final tests using our primary-key-counting test rig saw a 10 to 15% improvement over
Pulsing.

bq. I'm asking because I need his feature but I'm stuck with 3.x for a while. 

I have a client in a similar situation who are contemplating using the 3.6 patch.

bq. Is there bugs which should be fixed in initial 3.6 patch? 

It has been a while since I looked at it - a quick run of "ant test" on my copy here showed
no errors. I will be giving it a closer review if my client decides to go down this route
and can post any fixes here.
I expect if you use the patch and get into trouble you can use an un-patched version of 3.6
to read the same index files (it should just ignore the extra "blm" files created by the patched
version).

                
> Segment-level Bloom filters
> ---------------------------
>
>                 Key: LUCENE-4069
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4069
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: core/index
>    Affects Versions: 3.6, 4.0-ALPHA
>            Reporter: Mark Harwood
>            Assignee: Mark Harwood
>            Priority: Minor
>             Fix For: 4.0-BETA, 5.0
>
>         Attachments: 4069Failure.zip, BloomFilterPostingsBranch4x.patch, LUCENE-4069-tryDeleteDocument.patch,
LUCENE-4203.patch, MHBloomFilterOn3.6Branch.patch, PKLookupUpdatePerfTest.java, PKLookupUpdatePerfTest.java,
PKLookupUpdatePerfTest.java, PKLookupUpdatePerfTest.java, PrimaryKeyPerfTest40.java
>
>
> An addition to each segment which stores a Bloom filter for selected fields in order
to give fast-fail to term searches, helping avoid wasted disk access.
> Best suited for low-frequency fields e.g. primary keys on big indexes with many segments
but also speeds up general searching in my tests.
> Overview slideshow here: http://www.slideshare.net/MarkHarwood/lucene-bloomfilteredsegments
> Benchmarks based on Wikipedia content here: http://goo.gl/X7QqU
> Patch based on 3.6 codebase attached.
> There are no 3.6 API changes currently - to play just add a field with "_blm" on the
end of the name to invoke special indexing/querying capability. Clearly a new Field or schema
declaration(!) would need adding to APIs to configure the service properly.
> Also, a patch for Lucene4.0 codebase introducing a new PostingsFormat

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