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From Jake Mannix <jake.man...@gmail.com>
Subject Re: OutOfMemoryError when using Sort
Date Thu, 12 Nov 2009 16:41:55 GMT
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
>
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