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https://issues.apache.org/jira/browse/LUCENE-4574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13507045#comment-13507045
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Robert Muir commented on LUCENE-4574:
-------------------------------------
Just to bold what I said before, as I feel its important here:
{quote}
Finally, we could also consider something like your patch, except more honed in
these particular silly situations. so thats something like,
up-front setting a boolean in these collectors ctors if one of the comparators
is relevance *and also* its asked to track scores/max scores.
{quote}
Seems like we are doing it always if there is a relevance comparator? I feel
like the caching (which i hate) should be contained exactly to whats minimal
and necessary to prevent score from being called twice.
> FunctionQuery ValueSource value computed twice per document
> -----------------------------------------------------------
>
> Key: LUCENE-4574
> URL: https://issues.apache.org/jira/browse/LUCENE-4574
> Project: Lucene - Core
> Issue Type: Bug
> Components: core/search
> Affects Versions: 4.0, 4.1
> Reporter: David Smiley
> Attachments: LUCENE-4574.patch, LUCENE-4574.patch,
> Test_for_LUCENE-4574.patch
>
>
> I was working on a custom ValueSource and did some basic profiling and
> debugging to see if it was being used optimally. To my surprise, the value
> was being fetched twice per document in a row. This computation isn't
> exactly cheap to calculate so this is a big problem. I was able to
> work-around this problem trivially on my end by caching the last value with
> corresponding docid in my FunctionValues implementation.
> Here is an excerpt of the code path to the first execution:
> {noformat}
> at
> org.apache.lucene.queries.function.docvalues.DoubleDocValues.floatVal(DoubleDocValues.java:48)
> at
> org.apache.lucene.queries.function.FunctionQuery$AllScorer.score(FunctionQuery.java:153)
> at
> org.apache.lucene.search.TopFieldCollector$OneComparatorScoringMaxScoreCollector.collect(TopFieldCollector.java:291)
> at org.apache.lucene.search.Scorer.score(Scorer.java:62)
> at
> org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:588)
> at
> org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:280)
> {noformat}
> And here is the 2nd call:
> {noformat}
> at
> org.apache.lucene.queries.function.docvalues.DoubleDocValues.floatVal(DoubleDocValues.java:48)
> at
> org.apache.lucene.queries.function.FunctionQuery$AllScorer.score(FunctionQuery.java:153)
> at
> org.apache.lucene.search.ScoreCachingWrappingScorer.score(ScoreCachingWrappingScorer.java:56)
> at
> org.apache.lucene.search.FieldComparator$RelevanceComparator.copy(FieldComparator.java:951)
> at
> org.apache.lucene.search.TopFieldCollector$OneComparatorScoringMaxScoreCollector.collect(TopFieldCollector.java:312)
> at org.apache.lucene.search.Scorer.score(Scorer.java:62)
> at
> org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:588)
> at
> org.apache.lucene.search.IndexSearcher.search(IndexSearcher.java:280)
> {noformat}
> The 2nd call appears to use some score caching mechanism, which is all well
> and good, but that same mechanism wasn't used in the first call so there's no
> cached value to retrieve.
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