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From Peter Keegan <peterlkee...@gmail.com>
Subject Re: Use of AllTermDocs with custom scorer
Date Tue, 17 Nov 2009 13:58:18 GMT
The external data is just an array of fixed-length records, one for each
Lucene document. Indexes are updated at regular intervals in one jvm. A
searcher jvm opens the index and reads all the fixed-length records into
RAM. Given an index-wide docId, the custom scorer can quickly access the
corresponding fixed-length external data.

Could you explain a bit more about how mapping the external data to be per
segment would work? As I said, rebuilding the whole file isn't a big deal
and the single file keeps the Searcher's use of it simple.

With or without a SegmentReader->docBase map (which does sound like a huge
performance hit), I still don't see how the custom scorer gets the segment
number. Btw, the custom scorer usually becomes part of a ConjunctionScorer
(if that matters)

>FSHQ expects you to init it with the top-level reader, and then insert
using top docIDs.
For sorting, I'm using FSHQ directly with a custom collector that inserts
docs to the FSHQ. But the custom collector is passed the segment-relative
docId and the custom comparator needs the index-wide docId. The custom
collector extends HitCollector. I'm missing where this type of collector
finds the docBase.

Thanks,
Peter

On Tue, Nov 17, 2009 at 5:49 AM, Michael McCandless <
lucene@mikemccandless.com> wrote:

> On Mon, Nov 16, 2009 at 6:38 PM, Peter Keegan <peterlkeegan@gmail.com>
> wrote:
>
> >>Can you remap your external data to be per segment?
> >
> > That would provide the tightest integration but would require a major
> > redesign. Currently, the external data is in a single file created by
> > reading a stored field after the Lucene index has been committed.
> Creating
> > this file is very fast with 2.9 (considering the cost of reading all
> those
> > stored fields).
>
> OK.  Though if you update a few docs and open a new reader, you have
> to fully recreate the file?  (Or, your app may simply never need to do
> that...).
>
> >>For your custom sort comparator, are you using FieldComparator?
> >
> > I'm using the deprecated FieldSortedHitQueue. I started looking into
> > replacing it with FieldComparator, but it was much more involved than I
> had
> > expected, so I postponed. Also, this would only be a partial solution to
> a
> > query with a custom scorer and custom sorter.
>
> You are using FSHQ directly, yourself?  (Ie, not via TopFieldDocCollector)?
>
> FSHQ expects you to init it with the top-level reader, and then insert
> using top docIDs.
>
> >>Failing these, Lucene currently visits the readers in index order.
> >>So, you could accumulate the docBase by adding up the reader.maxDoc()
> >>for each reader you've seen.  However, this may change in future
> >>Lucene releases.
> >
> > This would work for the Scorer but not the Sorter, right?
>
> I don't fully understand the question -- the sorter is simply a
> Collector impl, and Collector.setNextReader tells you docBase when a
> the search advances to the next reader.
>
> >>You could also, externally, build your own map from SegmentReader ->
> >>docBase, by calling IndexReader.getSequentialSubReaders() and stepping
> >>through adding up the maxDoc.  Then, in your search, you can lookup
> >>the SegmentReader you're working on to get the docBase?
> >
> > I think this would work for both Scorer and Sorter, right?
> > This seems like the best solution right now.
>
> This is a generic solution, but just make sure you don't do the
> map lookup for every doc collected, if you can help it, else that'll
> slow down your search.
>
> Mike
>
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