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From "Anmol Bhasin" <>
Subject Re: docid set compression and boolean docid set operations
Date Sat, 13 Sep 2008 07:21:21 GMT

 Michael :

True, the table is a placeholder right now. I will run my performance
tests and update the table in the next day or two.

Paul :

 Thanks for skimming over the code. As John mentioned in his email, we
currently use Kamikaze for in memory caching for document hits. The
Kamikaze project is aimed to provide a docset implementation using
either an Integer array, an OpenBitSet or P4Delta data stucture using
the OpenBitSet(lucene)  depending on  the size and range of the
docset. There is a utility function exposed in
com.kamikaze.docidset.utils. which can decide on
the fly given the parameters as to what underlying datastructure
should be employed, however it is not tested thoroughly.

Moreover, we have implementations of Logic operators on the underlying
docsets which act like filters in Lucene. Again, these can be employed
to perform complex logic ops on the underlying docsets which in turn
could themselves be composite docsets generated using AND|OR|NOT
operations. The implementations do not materialize the interim or
final structures but simply expose an iterator to walk the docsets.

It would be wonderful if the indexing structure can be augumented
using Kamikaze. I can start
 proactively modifying/improving the implementation/packaging to ease
the process. As for storing the term frequencies and positions with
this datastructure, let me revisit the literature to see how best, if
at all we can assimilate them.

Thanks for the interest in Kamikaze and I would keep you posted once I
have updated performance numbers on the wiki.



On Thu, Sep 11, 2008 at 5:23 PM, John Wang <> wrote:
> Hi guys:
>     I will let the author, Anmol Bhasin to respond with details.
>     In our use case, we are not making changes to the index because we do
> not want to diverge from the lucene code base. (thought it'd be great if we
> can enhance indexing structure with this) We load the docIdSets into memory
> for caching reasons.
> Thanks
> -John
> On Thu, Sep 11, 2008 at 3:28 AM, Paul Elschot <>
> wrote:
>> John,
>> I've taken a first look at the code, and I have a few questions.
>> Did I understand correctly that it is basically a two way
>> conversion between an integer array and an (Open)BitSet
>> representing a p4delta data structure?
>> In that case it would still be necessary to extend the lucene
>> index structure to make it understand the p4delta data structure
>> at the appropriate places.
>> I can help getting the code integrated into lucene, but I've
>> never done an index structure extension, so I'd like to have
>> some support from this list for that.
>> The code would initially need some package restructuring and
>> layout changes, and then it could move forward to an index
>> structure extension.
>> Would you have some ideas on how to use de p4delta structure
>> to store docIds, term frequencies and term positions?
>> The references give some insights there, but it seems that there
>> is still quite a bit of work to do get such "details" right.
>> Fortunately, the existing Lucene TermDocs and TermPositions
>> appear to be just right for this.
>> Regards,
>> Paul Elschot
>> Op Wednesday 10 September 2008 23:09:18 schreef John Wang:
>> > Sorry, I meant lucene 2.4
>> >
>> > -John
>> >
>> > On Wed, Sep 10, 2008 at 2:08 PM, John Wang <>
>> wrote:
>> > > Hi guys:
>> > >
>> > >      We have build this on top of the lucene 1.4. api/refactoring
>> > > for docid sets and docIdIterater.
>> > >
>> > >      We've implemented the p4Delta compression algorithm presented
>> > > at www2008:
>> > >
>> > >      We've been using this in production here at LinkedIn and would
>> > > love to contribute it into lucene.
>> > >
>> > >      We currently open sourced it at:
>> > >
>> > >
>> > >      Please let us know if it is thing you guys want to proceed, if
>> > > so, what are the steps we should take.
>> > >
>> > > Thanks
>> > >
>> > > -John
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Courage doesn't always roar. Sometimes courage is the quiet voice at
the end of the day saying, "I will try again tomorrow"

Anmol Bhasin
SSE Data Platform

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