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https://issues.apache.org/jira/browse/LUCENE-1593?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12704692#action_12704692
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Michael McCandless commented on LUCENE-1593:
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bq. What will TermQuery do?
Oh: it's fine to return an in-order scorer, always. It's just that if
a Query wants to use an out-of-order scorer, it should also implement
an in-order one. Ie, there'd be a "mating process" to match the
scorer to the collector.
That that there might be a Collector out there that requires docs in order is
not something I think we should handle. Reason is, there wasn't any guarantee
until today that docs are returned in order. So how can somehow write a
Collector which has a hard assumption on that? Maybe only if he used a Query
which he knows always scores in order, such as TQ, but then I don't think this
guy will have a problem since TQ returns true.
bq. And if that someone needs docs in order, but the query at hand returns docs
out of order, then I'd say tough luck ? I mean, maybe with BQ we can ensure
in/out of order on request, but if there will be a query which returns docs in
random, or based on other criteria which causes it to return out of order, what
good will forcing it to return docs in order do? I'd say that you should just
use a different query in that case?
Well... we have to be careful. EG say we had some great optimization
for iterating over matches to PhraseQuery, but it returned docs out of
order. In that case, I think we'd preserve the in-order Scorer as
well?
bq. But I'm not sure in practice when one would want to use an out-of-order
non-top iterator.
One case might be a random access filter AND'd w/ a BooleanQuery. In
that case I could ask for a BooleanScorer to return a DISI whose next
is allowed to return docs out of order, because 1) my filter doesn't
care and 2) my collector doesn't care.
Though, we are thinking about pushing random access filters all the
way down to the TermScorer, so this is example isn't realistic in that
future... but it still feels like "out of order iteration" and "I'm
top scorer or not" are orthogonal concepts.
> Optimizations to TopScoreDocCollector and TopFieldCollector
> -----------------------------------------------------------
>
> Key: LUCENE-1593
> URL: https://issues.apache.org/jira/browse/LUCENE-1593
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Reporter: Shai Erera
> Fix For: 2.9
>
> Attachments: LUCENE-1593.patch, LUCENE-1593.patch, PerfTest.java
>
>
> This is a spin-off of LUCENE-1575 and proposes to optimize TSDC and TFC code
> to remove unnecessary checks. The plan is:
> # Ensure that IndexSearcher returns segements in increasing doc Id order,
> instead of numDocs().
> # Change TSDC and TFC's code to not use the doc id as a tie breaker. New docs
> will always have larger ids and therefore cannot compete.
> # Pre-populate HitQueue with sentinel values in TSDC (score = Float.NEG_INF)
> and remove the check if reusableSD == null.
> # Also move to use "changing top" and then call adjustTop(), in case we
> update the queue.
> # some methods in Sort explicitly add SortField.FIELD_DOC as a "tie breaker"
> for the last SortField. But, doing so should not be necessary (since we
> already break ties by docID), and is in fact less efficient (once the above
> optimization is in).
> # Investigate PQ - can we deprecate insert() and have only
> insertWithOverflow()? Add a addDummyObjects method which will populate the
> queue without "arranging" it, just store the objects in the array (this can
> be used to pre-populate sentinel values)?
> I will post a patch as well as some perf measurements as soon as I have them.
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