> Now I have another question... is there a way to specify a "start from" so > I > could get page 2, 3, 4, etc.. ?
Search the mailing list, this was explained quite often (by others and me). The trick is: If you have 200 results per page, with n = 200 you get the top ranking results for the first page. If you want to have the second page, reexecute the query with n=400 and display scoreDocs[200..399] and so on. All full text engines work like this, they can only collect top-mathcing documents, but no documents in a slot. If n gets too big it gets very slow and uses too much memory. Because of that, Google limits the maximum page number. > On Mon, Nov 30, 2009 at 12:00 PM, Uwe Schindler <u...@thetaphi.de> wrote: > > > > 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: u...@thetaphi.de > > > > > > > -----Original Message----- > > > > From: Michel Nadeau [mailto:aka...@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 > > > > aka...@gmail.com > > > > > > > > > > > > On Mon, Nov 30, 2009 at 11:30 AM, Erick Erickson > > > > <erickerick...@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 <aka...@gmail.com> > > > > wrote: > > > > > > > > > > > What is the main difference between Hits and Collectors? > > > > > > > > > > > > - Mike > > > > > > aka...@gmail.com > > > > > > > > > > > > > > > > > > On Mon, Nov 30, 2009 at 11:03 AM, Uwe Schindler > <u...@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: u...@thetaphi.de > > > > > > > > > > > > > > > > > > > > > > -----Original Message----- > > > > > > > > From: Shai Erera [mailto:ser...@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 > > > <aka...@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 > > > > > > > > > aka...@gmail.com > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ------------------------------------------------------------------ > > > -- > > > > - > > > > > > > To unsubscribe, e-mail: java-user- > unsubscr...@lucene.apache.org > > > > > > > For additional commands, e-mail: > > java-user-h...@lucene.apache.org > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > --------------------------------------------------------------------- > > > To unsubscribe, e-mail: java-user-unsubscr...@lucene.apache.org > > > For additional commands, e-mail: java-user-h...@lucene.apache.org > > > > > > > > --------------------------------------------------------------------- > > To unsubscribe, e-mail: java-user-unsubscr...@lucene.apache.org > > For additional commands, e-mail: java-user-h...@lucene.apache.org > > > > --------------------------------------------------------------------- To unsubscribe, e-mail: java-user-unsubscr...@lucene.apache.org For additional commands, e-mail: java-user-h...@lucene.apache.org
