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From Peter Keegan <peterlkee...@gmail.com>
Subject Re: Use of AllTermDocs with custom scorer
Date Tue, 17 Nov 2009 15:23:52 GMT
>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.

What I just learned is that a Scorer is created for each segment (lights
on!).
So, couldn't I just do the subreader->docBase map lookup once when the
custom scorer is created? No need to access the map for every doc this way.

Peter

On Tue, Nov 17, 2009 at 8:58 AM, Peter Keegan <peterlkeegan@gmail.com>wrote:

> 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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>>
>

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