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From "Uwe Schindler" <...@thetaphi.de>
Subject RE: Performance problems with Lucene 2.9
Date Mon, 30 Nov 2009 17:00:15 GMT
> And sorting is done by the
> collector, Lucene has no idea how to sort.

Sorting is done by the internal collector behind the
Top(Field)Docs-returning method (your own collectors would have to do it
themselves). If you call search(Query, n,... Sort), internally an collector
is created that does the sorting for you and throws away all results that do
not fall into the first 200 hits (if n=200).

> If you use Sort, the returned
> TopDocs will be sorted.
> 
> If you do not sort at all and do not score your results, TopDocs is not
> very
> useful, because the first 200 hits cannot be ranked.
> 
> -----
> Uwe Schindler
> H.-H.-Meier-Allee 63, D-28213 Bremen
> http://www.thetaphi.de
> eMail: uwe@thetaphi.de
> 
> > -----Original Message-----
> > From: Michel Nadeau [mailto:akaris@gmail.com]
> > Sent: Monday, November 30, 2009 5:35 PM
> > To: java-user@lucene.apache.org
> > Subject: Re: Performance problems with Lucene 2.9
> >
> > I'll definitely switch to a Collector.
> >
> > It's just not clear for me if I should use BooleanQueries or
> > MatchAllDocuments+Filters ?
> >
> > And should I write my own collector or the TopDocs one is perfect for me
> ?
> >
> > - Mike
> > akaris@gmail.com
> >
> >
> > On Mon, Nov 30, 2009 at 11:30 AM, Erick Erickson
> > <erickerickson@gmail.com>wrote:
> >
> > > The problem with hits is that a it re-executes the query
> > > every N documents where N is 100 (?).
> > >
> > > So, a loop like
> > > for (int idx : hits.length) {
> > >   do something....
> > > }
> > >
> > > Assuming my memory is right and it's every 100, your query will
> > > re-execute (length/100) times. Which is unfortunate.
> > >
> > > The very quick test to see where to concentrate first would be to take
> > > a time stamp just before you hit your loop.....
> > >
> > > This will tell you whether this loop is the culprit, but it really
> > doesn't
> > > matter because you'll follow the advice from Uwe and Shai anyway <G>.
> > >
> > > Filtering and Sorting are applied to Collectors before you see
> them.....
> > >
> > > The other bit would be to investigate your sorting. Remember that the
> > > first sort or two take quite a while since the relevant caches are
> > > populated with first used, so second+ queries should be faster. The
> > > Wiki has some timing/speedup advice.....
> > >
> > > Best
> > > Erick
> > >
> > >
> > > On Mon, Nov 30, 2009 at 11:10 AM, Michel Nadeau <akaris@gmail.com>
> > wrote:
> > >
> > > > What is the main difference between Hits and Collectors?
> > > >
> > > > - Mike
> > > > akaris@gmail.com
> > > >
> > > >
> > > > On Mon, Nov 30, 2009 at 11:03 AM, Uwe Schindler <uwe@thetaphi.de>
> > wrote:
> > > >
> > > > > And if you only have a filter and apply it to all documents, make
> a
> > > > > ConstantScoreQuery on top of the filter:
> > > > >
> > > > > Query q=new ConstantScoreQuery(cluCF);
> > > > >
> > > > > Then remove the filter from your search method call and only
> execute
> > > this
> > > > > query.
> > > > >
> > > > > And if you iterate over all results never-ever use Hits! (its
> > already
> > > > > deprecated). Write a Collector instead (as you are not interested
> in
> > > > > scoring).
> > > > >
> > > > > And: If you replace a relational database with Lucene, be sure not
> > to
> > > > think
> > > > > in a relational sense with foreign keys / primary keys and so on.
> In
> > > > > general
> > > > > you should flatten everything.
> > > > >
> > > > > Uwe
> > > > >
> > > > > -----
> > > > > Uwe Schindler
> > > > > H.-H.-Meier-Allee 63, D-28213 Bremen
> > > > > http://www.thetaphi.de
> > > > > eMail: uwe@thetaphi.de
> > > > >
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Shai Erera [mailto:serera@gmail.com]
> > > > > > Sent: Monday, November 30, 2009 4:56 PM
> > > > > > To: java-user@lucene.apache.org
> > > > > > Subject: Re: Performance problems with Lucene 2.9
> > > > > >
> > > > > > Hi
> > > > > >
> > > > > > First you can use MatchAllDocsQuery, which matches all
> documents.
> > It
> > > > will
> > > > > > save a HUGE posting list (TAG:TAG), and performs much faster.
> For
> > > > example
> > > > > > TAG:TAG computes a score for each doc, even though you don't
> need
> > it.
> > > > > > MatchAllDocsQuery doesn't.
> > > > > >
> > > > > > Second, move away from Hits ! :) Use Collectors instead.
> > > > > >
> > > > > > If I understand the chain of filters, do you think you can code
> > them
> > > > with
> > > > > > a
> > > > > > BooleanQuery that is added BooleanClauses, each with is Term
> > > > > > (field:value)?
> > > > > > You can add clauses w/ OR, AND, NOT etc.
> > > > > >
> > > > > > Note that in Lucene 2.9, you can avoid scoring documents very
> > easily,
> > > > > > which
> > > > > > is a performance win if you don't need scores (i.e. if you just
> > want
> > > to
> > > > > > match everything, not caring for scores).
> > > > > >
> > > > > > Shai
> > > > > >
> > > > > > On Mon, Nov 30, 2009 at 5:47 PM, Michel Nadeau
> <akaris@gmail.com>
> > > > wrote:
> > > > > >
> > > > > > > Hi,
> > > > > > >
> > > > > > > we use Lucene to store around 300 millions of records.
We use
> > the
> > > > index
> > > > > > > both
> > > > > > > for conventional searching, but also for all the system's
data
> -
> > we
> > > > > > > replaced
> > > > > > > MySQL with Lucene because it was simply not working at
all
> with
> > > MySQL
> > > > > > due
> > > > > > > to
> > > > > > > the amount or records. Our problem is that we have HUGE
> > performance
> > > > > > > problems... whenever we search, it takes forever to return
> > results,
> > > > and
> > > > > > > Java
> > > > > > > uses 100% CPU/RAM.
> > > > > > >
> > > > > > > Our index fields are like this:
> > > > > > >
> > > > > > > TYPE
> > > > > > > PK
> > > > > > > FOREIGN_PK
> > > > > > > TAG
> > > > > > > ...other information depending on type...
> > > > > > >
> > > > > > > * All fields are Field.Index.UN_TOKENIZED
> > > > > > > * The field "TAG" always contains the value "TAG".
> > > > > > >
> > > > > > > Whenever we search in the index, our query is "TAG:TAG"
to
> match
> > > all
> > > > > > > documents, and we do the search like this:
> > > > > > >
> > > > > > >        // Search
> > > > > > >        Hits h = searcher.search(q, cluCF, cluSort);
> > > > > > >
> > > > > > > cluCF is a ChainedFilter containing all the other filters
> (like
> > > > > > > FOREIGN_PK=12345, TYPE=a, etc.).
> > > > > > >
> > > > > > > I know that the method is probably crazy because "TAG:TAG"
is
> > > > matching
> > > > > > all
> > > > > > > 300M documents and then it applies filters; so that's probably
> > why
> > > > > every
> > > > > > > little query is taking 100% CPU/RAM.... but I don't know
how
> to
> > do
> > > it
> > > > > > > properly.
> > > > > > >
> > > > > > > Help ! Any advice is welcome.
> > > > > > >
> > > > > > > - Mike
> > > > > > > akaris@gmail.com
> > > > > > >
> > > > >
> > > > >
> > > > > ------------------------------------------------------------------
> --
> > -
> > > > > 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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