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From Shai Erera <ser...@gmail.com>
Subject Re: Bug in TopFieldCollector?
Date Mon, 30 Mar 2009 10:47:26 GMT
I checked where it is used, and this arg is required by FieldValueHitQueue,
by its only constructor. The array is passed to each field's getComparator
method, which uses it only for CUSTOM field indeed. There, it calls
comparatorSource.newComparator, and there's only one implementation now of
it, which ignores it entirely.
So it looks this can be easily removed.

I also added a line before construction of FieldValueHitQueue which
nullifies the array, and the tests in TestSort pass. So this convinces me
even more we can remove it.

I remvoed it and nothing breaks (compilation-wise), so I'll proceed with it
as part of 1575.

On Mon, Mar 30, 2009 at 11:49 AM, Uwe Schindler <uwe@thetaphi.de> wrote:

> You are right, I forget the sorting. And I also think, the most important
> thing would be to remove the need for the ctor in the custom sort.
>
> -----
> Uwe Schindler
> H.-H.-Meier-Allee 63, D-28213 Bremen
> http://www.thetaphi.de
> eMail: uwe@thetaphi.de
>
> > -----Original Message-----
> > From: Michael McCandless [mailto:lucene@mikemccandless.com]
> > Sent: Monday, March 30, 2009 10:44 AM
> > To: java-dev@lucene.apache.org
> > Subject: Re: Bug in TopFieldCollector?
> >
> > Well, IndexSearcher also sorts its readers biggest to smallest (by
> > .numDocs()) for better performance (so that the queues fill up as much
> > as possible before hitting reader transitions).
> >
> > I think it's the exception, not the rule, for when a custom comparator
> > would require the full array of sub-readers up front (vs, "on the fly"
> > which it already gets with setNextReader), so I think we should not
> > pass it in during construction.
> >
> > This really was a rote carryover from the old API which passed in the
> > top IndexReader when calling newComparator.
> >
> > Mike
> >
> > On Mon, Mar 30, 2009 at 4:39 AM, Uwe Schindler <uwe@thetaphi.de> wrote:
> > > Why not call IndexSearcher.getIndexReader().getSequentialSubReaders()
> > (see
> > > http://hudson.zones.apache.org/hudson/job/Lucene-
> > trunk/javadoc/all/org/apache/lucene/index/IndexReader.html).
> > > Its public and documented as this:
> > >
> > >
> > >
> > > public IndexReader[] getSequentialSubReaders()
> > >
> > >
> > >
> > > Expert: returns the sequential sub readers that this reader is
> logically
> > > composed of. For example, IndexSearcher uses this API to drive
> searching
> > by
> > > one sub reader at a time. If this reader is not composed of sequential
> > child
> > > readers, it should return null. If this method returns an empty array,
> > that
> > > means this reader is a null reader (for example a MultiReader that has
> > no
> > > sub readers).
> > >
> > > NOTE: for a MultiSegmentReader, which is obtained by
> > open(java.lang.String)
> > > when the index has more than one segment, you should not use the sub-
> > readers
> > > returned by this method to make any changes (setNorm, deleteDocument,
> > etc.).
> > > Doing so will likely lead to index corruption. Use the parent reader
> > > instead.
> > >
> > >
> > >
> > > You only have the problem to replicate the code that gathers the
> > subreaders
> > > of the subreaders itself recursively.
> > >
> > >
> > >
> > > Uwe
> > >
> > > -----
> > > Uwe Schindler
> > > H.-H.-Meier-Allee 63, D-28213 Bremen
> > > http://www.thetaphi.de
> > > eMail: uwe@thetaphi.de
> > >
> > > ________________________________
> > >
> > > From: Shai Erera [mailto:serera@gmail.com]
> > > Sent: Monday, March 30, 2009 10:20 AM
> > > To: java-dev@lucene.apache.org
> > > Subject: Re: Bug in TopFieldCollector?
> > >
> > >
> > >
> > > Already did !
> > >
> > > Another question - I think we somehow broke TopFieldCollector ...
> > > Previously, in TopFieldDocCollector, it accepted an IndexReader as a
> > > parameter, and now it requires IndexReader[], which is called
> > subReaders.
> > > Calling the 'fast' search methods with Sort has no problem obtaining
> > that
> > > IndexReader[] (and sort it), but how would someone use
> TopFieldCollector
> > w/o
> > > calling the appropriate Searcher methods?
> > >
> > > For example, since all the Searcher methods pass in fillFields = true,
> I
> > > wanted to use the method Searcher.search(Query, TopFieldCollector) in
> > the
> > > test case I wrote, which BTW looks like this:
> > >
> > >   public void testSortWithoutFillFields() throws Exception {
> > >
> > >     // There was previously a bug in TopFieldCollector when fillFields
> > was
> > > set
> > >     // to false - the same doc and score was set in ScoreDoc[] array.
> > This
> > > test
> > >     // asserts that if fillFields is false, the documents are set
> > properly.
> > > It
> > >     // does not use Searcher's default search methods (with Sort) since
> > all
> > > set
> > >     // fillFields to true.
> > >     Sort sort = new Sort();
> > >     int nDocs=10;
> > >
> > >     TopDocsCollector tdc = new TopFieldCollector(sort, nDocs,
> > >         new IndexReader[] { ((IndexSearcher) full).getIndexReader() },
> > > false);
> > >
> > >     full.search(new MatchAllDocsQuery(), tdc);
> > >
> > >     ScoreDoc[] sd = tdc.topDocs().scoreDocs;
> > >     for (int i = 1; i < sd.length; i++) {
> > >       assertTrue(sd[i].doc != sd[i - 1].doc);
> > >     }
> > >   }
> > >
> > > You'll notice that creating a TopFieldCollector now is much more
> > complicated
> > > and *ugly*. As a user of IndexSearcher, I can only call
> getIndexReader()
> > > which returns a single IndexReader. I don't have access to
> > gatherSubReaders
> > > and sortSubReaders. I don't see why I should have access to them. So it
> > > forces me to create a dummy array with a single IndexReader.
> > >
> > > There are two ways I see to solve it:
> > > 1. Introduce a getIndexReaders() method on IndexSearcher, which will
> > return
> > > an array of (sorted?) IndexReader.
> > > 2. Introduce a new constructor in TopFieldCollector which accepts a
> > single
> > > IndexReader and make the other one package-private (for use by
> > IndexSearcher
> > > only). That constructor can internally create a dummy array of readers,
> > but
> > > at least it's private to the constructor and not exposed to the rest of
> > the
> > > world.
> > >
> > > Otherwise, I think it ruins TopFieldCollector and will make it a lot
> > less
> > > intuitive to use. At least, people who'd want to move from
> > > TopFieldDocCollector to TopFieldCollector, will find it very
> > inconvenient
> > > and strange.
> > >
> > > What do you think? I can do that (2) as part of 1575. If (1) is better,
> > then
> > > I think a different issue should be opened, because we might want to
> > return
> > > such an array as sorted or something, which makes it less trivial.
> > >
> > > Shai
> > >
> > > On Mon, Mar 30, 2009 at 11:07 AM, Michael McCandless
> > > <lucene@mikemccandless.com> wrote:
> > >
> > > Looks like quite a bug, Shai!  Thanks.  It came in with LUCENE-1483.
> > > I would say add test case & fix it under 1575.
> > >
> > > Mike
> > >
> > > On Mon, Mar 30, 2009 at 3:50 AM, Shai Erera <serera@gmail.com> wrote:
> > >> Hi
> > >>
> > >> As I prepared the patch for 1575, I noticed a strange implementation
> in
> > >> TopFieldCollector's topDocs():
> > >>
> > >>     ScoreDoc[] scoreDocs = new ScoreDoc[queue.size()];
> > >>     if (fillFields) {
> > >>       for (int i = queue.size() - 1; i >= 0; i--) {
> > >>         scoreDocs[i] = queue.fillFields((FieldValueHitQueue.Entry)
> > >> queue.pop());
> > >>       }
> > >>     } else {
> > >>       Entry entry = (FieldValueHitQueue.Entry) queue.pop();
> > >>       for (int i = queue.size() - 1; i >= 0; i--) {
> > >>         scoreDocs[i] = new FieldDoc(entry.docID,
> > >>                                     entry.score);
> > >>       }
> > >>     }
> > >>
> > >>     return new TopFieldDocs(totalHits, scoreDocs, queue.getFields(),
> > >> maxScore);
> > >>
> > >>
> > >> Notice that if fillFields is true, then documents are popped from the
> > >> queue.
> > >> However if it's false, then the first document is popped out of the
> > queue
> > >> and used to populate the entire ScoreDoc[]? I believe that's wrong,
> > right?
> > >> Otherwise, the returned TopFieldDocs.scoreDocs array will include the
> > same
> > >> document and score?
> > >>
> > >> I noticed there's no test case for that ... TopFieldCollector's
> > >> constructor
> > >> is called only from IndexSearcher.search(Weight, Filter, int, Sort,
> > >> boolean
> > >> /* fillFields */) which is called from IndexSearcher.search(Weight,
> > >> Filter,
> > >> int, sort) with fillFields always set to true. So perhaps that's why
> > this
> > >> hasn't showed up?
> > >>
> > >> BTW, the now deprecated TopFieldDocCollector's topDocs()
> implementation
> > >> looks like this:
> > >>
> > >>     FieldSortedHitQueue fshq = (FieldSortedHitQueue)hq;
> > >>     ScoreDoc[] scoreDocs = new ScoreDoc[fshq.size()];
> > >>     for (int i = fshq.size()-1; i >= 0; i--)      // put docs in array
> > >>       scoreDocs[i] = fshq.fillFields ((FieldDoc) fshq.pop());
> > >>
> > >>     return new TopFieldDocs(totalHits, scoreDocs,
> > >>                             fshq.getFields(), fshq.getMaxScore());
> > >>
> > >> It assumes fillFields is always true and always pops elements out of
> > the
> > >> queue.
> > >>
> > >> If this is a bug, I can fix it as part of 1575, as I'm touching that
> > class
> > >> anyway. I can also add a test case ... The fix is very simple BTW,
> just
> > >> move
> > >> the line "Entry entry = (FieldValueHitQueue.Entry) queue.pop();"
> inside
> > >> the
> > >> for loop.
> > >>
> > >> Shai
> > >>
> > >
> > > ---------------------------------------------------------------------
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> > > For additional commands, e-mail: java-dev-help@lucene.apache.org
> > >
> > >
> >
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>
>
>
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