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From "John Wang" <john.w...@gmail.com>
Subject Re: docid set compression and boolean docid set operations
Date Mon, 15 Sep 2008 16:58:50 GMT
HI Paul and Eks:
     Thanks for your responses.

     Kamikaze is split into 2 parts: compression(p4delta) and set boolean
logic docIdSet iterators (OR, AND, NOT).

     I do see the patch for the DisjunctionDocsetIterator, I agree that
there is no need to replicate the effort. What about AND and NOT? Also, do
you know when these patches will be applied?

    Are you guys interested in helping out on kamikaze?

Thanks

-John

On Sat, Sep 13, 2008 at 1:45 AM, Paul Elschot <paul.elschot@xs4all.nl>wrote:

>
> Op Saturday 13 September 2008 09:21:21 schreef Anmol Bhasin:
> > Hi,
> >
> >  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. DocSetFactory.java which can decide on
> > the fly given the parameters as to what underlying datastructure
> > should be employed, however it is not tested thoroughly.
>
> Such a factory is precisely what is left open here:
> https://issues.apache.org/jira/browse/LUCENE-1296
> Basically, we need a subclass of CachingWrapperFilter to implement
> such a factory.
>
> >
> > 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.
>
> Further to what Eks said, the patch at LUCENE-1345 extends
> existing lucene scorers to walk docsets. It does this by allowing
> a mix of DocIdSetIterators (for Filters) and Scorers (for Queries).
> The class structure for this is still in its infancy, I'm trying to
> figure out how much inheritance to use to implement the
> various Scorers as subclasses of DocIdSetIterators.
>
> > 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.
>
> Be sure to take small steps. The p4delta code from kamikaze that I
> have seen so far still needs some performance improvements.
> For example the main decompression loop contains an if statement
> for the exceptions, but the whole point of p4delta decompression is
> it to avoid that. Nevertheless, this implementation has the advantage
> of being relatively easy to understand, so it could be very useful for
> testing.
> I don't know whether I have seen all of the code, though.
>
> > 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.
>
> This fits nicely with the recent flexible indexing efforts.
> Most of the performance improvements are are reported from the
> positions, so we might try and start there. Alternatively, to get going,
> the p4delta data structure might be initially used to support boolean
> docid set operations.
>
> Regards,
> Paul Elschot
>
>
> > Thanks for the interest in Kamikaze and I would keep you posted once
> > I have updated performance numbers on the wiki.
> >
> > Thanks,
> > Anmol
> >
> >
> >
> >
> >
> > com.kamikaze.docidset.utils
> >
> > On Thu, Sep 11, 2008 at 5:23 PM, John Wang <john.wang@gmail.com>
> 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
> > > <paul.elschot@xs4all.nl>
> > >
> > > 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 <john.wang@gmail.com>
> > >>
> > >> 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: http://www2008.org/papers/fp618.html
> > >> > >
> > >> > >      We've been using this in production here at LinkedIn and
> > >> > > would love to contribute it into lucene.
> > >> > >
> > >> > >      We currently open sourced it at:
> > >> > > http://code.google.com/p/lucene-ext/wiki/Kamikaze
> > >> > >
> > >> > >      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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>
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