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From "Uwe Schindler" <...@thetaphi.de>
Subject RE: OutOfMemoryError when using Sort
Date Thu, 12 Nov 2009 17:45:42 GMT
I am not really sure, why it is enough for you to sort the first 50 highest
ranking hits, but if you only want to do this, sorting afterwards is quite
straightforward.

Another idea is to not index the count itself, but more use the count as a
boost factor for each document. The ranking algorithm of lucene will then
boost docs with higher counts to the top results. But notice: The boost is
combined with the already available boots (multiplied), so the sorting will
be a combination of boost and native lucene rank. You can try to overcome
that by scaling the boost very large (factor 10 or so should be enough for
5-grams).

-----
Uwe Schindler
H.-H.-Meier-Allee 63, D-28213 Bremen
http://www.thetaphi.de
eMail: uwe@thetaphi.de

> -----Original Message-----
> From: Nuno Seco [mailto:nseco@dei.uc.pt]
> Sent: Thursday, November 12, 2009 6:08 PM
> To: java-user@lucene.apache.org
> Subject: Re: OutOfMemoryError when using Sort
> 
> Ok. Thanks.
> 
> The doc. says:
> "Finds the top |n| hits for |query|, applying |filter| if non-null, and
> sorting the hits by the criteria in |sort|."
> 
> I understood that only the hits (50 in this) for the current search
> would be sorted...
> I'll just do the ordering afterwards. Thank you for clarifying this issue.
> 
> 
> --
> Nuno Seco
> 
> 
> Jake Mannix wrote:
> > Sorting utilizes a FieldCache: the forward lookup - the value a document
> has
> > for a
> > particular field (as opposed to the usual "inverted" way of looking at
> all
> > documents
> > which contains a given term), which lives in memory, and takes up as
> much
> > space
> > as one 4-bytes * numDocs.
> >
> > If you've indexed the entire 5Gram data set on one index, on one
> machine,
> > you've
> > got how many documents?  Billions?  This will take up billions*4bytes of
> RAM
> > to
> > do this sort.
> >
> > You need to shard your index (break it up onto multiple machines, do
> your
> > sort
> > distributed, and merge the results) if you want to do this sorting with
> any
> > kind
> > of performance.
> >
> >   -jake
> >
> > On Thu, Nov 12, 2009 at 7:57 AM, Nuno Seco <nseco@dei.uc.pt> wrote:
> >
> >
> >> Hello List.
> >>
> >> I'm having a problem when I add a Sort object to my searcher:
> >>   docs = searcher.search(parser.parse(search), null, 50, sort);
> >>
> >> Every time I execute a query I get an OutOfMemoryError exception.
> >> But if I execute the query without the Sort object it works fine
> >>
> >> Let me briefly explain how my index is structured.
> >> I'm indexing the Google 5Grams
> >> (
> >> http://googleresearch.blogspot.com/2006/08/all-our-n-gram-are-belong-
> to-you.html).
> >>
> >> The index just has two fields:
> >>   data = new Field("data", tokens[0], Field.Store.YES,
> >> Field.Index.ANALYZED, Field.TermVector.NO);
> >>   count = new Field("count", tokens[1], Field.Store.YES,
> >> Field.Index.NO, Field.TermVector.NO);
> >>
> >> the data corresponds to the 5 gram; e.g.: "my business manager informed
> me"
> >> and the count is simply an integer that represents the frequency of the
> >> ngram.
> >>
> >> The index size after optimization is 63G.
> >>
> >> If I do not store the data field using:
> >>   data = new Field("data", tokens[0], Field.Store.NO,
> >> Field.Index.ANALYZED, Field.TermVector.NO);
> >> the total size drops to 32G
> >>
> >>
> >> But using either index with the Sort object causes the exception. I'm
> >> creating the Sort object like:
> >>   Sort sort = new Sort(new SortField("count", SortField.INT));
> >>
> >> Note: That even with out using the Sort object I still need to pump the
> >> jvm to 2G (-Xmx2048m). But thats ok...
> >>
> >>
> >> So.... Basically what I want is to order those first 50 hits I get
> >> according to their frequency counts (count field).
> >>
> >>
> >> I'm using:
> >> java version "1.6.0_16" (64 bit)
> >> lucene 2.9.1
> >> linux ext3 FS
> >> linux kernel 2.6.31-15
> >>
> >> Can anybody help me or redirect me in the right direction?
> >>
> >> Thanks
> >>
> >> --
> >> Nuno Seco
> >>
> >> ---------------------------------------------------------------------
> >> To unsubscribe, e-mail: java-user-unsubscribe@lucene.apache.org
> >> For additional commands, e-mail: java-user-help@lucene.apache.org
> >>
> >>
> >>
> >
> >
> 
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