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From mark harwood <>
Subject Re: Long Query Performance
Date Mon, 22 Jan 2007 14:36:45 GMT
"" is in the "contrib" section of SVN and this will help optimise your queries
to searching for only the most discriminating terms.
On a large index, very common terms can really kill performance (reading lots of docIds from
disk) and the MoreLikeThis class will help to trim your query terms down to avoid such words.

This will still take some time to run but at least the job sounds like one that can easily
be split to run in parallel on multiple machines (assuming you have some to hand!)


----- Original Message ----
From: Somnath Banerjee <>
Sent: Monday, 22 January, 2007 1:28:20 PM
Subject: Re: Long Query Performance

Thanks for the reply. Good guess I think.

DB (Index) is basically a collection of encyclopedia documents. Queries are
also a collection of documents but of various domains. My task is to find
out for each "query document" top 100 matching encyclopedia contents.

I tried by using only the title of (5-8 words) the query documents instead
of full text of the document. But that is also taking 0.5-1 sec for each
query. That's mean it will also take nearly 6 and half days to run
0.72Mqueries (and expectedly the precision will suffer).


On 1/22/07, Michael D. Curtin <> wrote:
> Somnath Banerjee wrote:
> >            I have created a 8GB index of almost 2 million documents. My
> > requirement is to run nearly 0.72 million query on this index. Each
> query
> > consists of 200 - 400 words. I have created a Boolean Query by ORing
> these
> > words. But each query is taking nearly 5 - 10 seconds to execute ( 2.78
> > GHz,
> > 1.5 GB RAM). That's mean the entire batch of 0.72M query will take more
> > than
> > 70 days to execute. Is it expected or there is a way to improve the
> > performance? From earlier posts I gathered that complex query is
> > expected to
> > take more time (this much???).
> A back of the envelope calculation:
>      8GB / 2M docs = 4KB per doc, on avg
>                    / 5 B per word, on avg = 800 words per doc, on avg
> So, each query is a quarter to half the size of the average document.  I
> suspect that just about every query is hitting almost every document in
> the db, i.e. the queries are not very selective at all.  That's going to
> be slow, no two ways about it.
> Could you tell us a bit more about the db and what your application is
> looking for in it, at a higher level of abstraction?
> --MDC
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