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https://issues.apache.org/jira/browse/LUCENE-4574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13507499#comment-13507499
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Robert Muir commented on LUCENE-4574:
-------------------------------------
{quote}
So why do you hate this very simple cache so much?
{quote}
I want things fixed correctly, the way I see it there is a lot of bogusness:
* When solr is only sorting by score, it should call IS.search without a Sort
to get faster behavior. The relevance comparator documents that its the slow
way.
* its especially stupid someone can ask for fillFields=true and
trackDocScores=true if you have a relevance comparator.
* i'm not sure trackMaxScore=true is really useful at all except when relevance
is the only sort, in which case you should be using IS.search without a sort
anyway. If someone really needs this combination, i think its ok to make them
impl their own collector
* i don't like wrapping the scorer with this cache in this relevance
comparator. I feel like the comparator can probably do this in a cleaner way.
* i don't like all this caching just added on a whim everywhere. I see it here,
I see BooleanScorer2 has a cache, I see block-join query has a cache, and I see
PositivesScoreOnlyCollector has a cache. there are already cachingvaluesources
at the valuesource level too: look at CachingDoubleValueSource in spatial .Some
of these are senseless. If there is a real reason, its not documented. We
should instead fix the APIs and so on instead of just adding all this caching
everywhere.
* i think calling score() twice is bogus, but we should be fixing this
correctly instead of hacking something in to speed up a slow functionquery.
So yeah, clearly adding caches everywhere isn't the right solution to this
stuff. I feel like I'm drowning in caches and bug reports like this one still
exist.
We shouldnt rush anything in because of a particularly slow function query.
Trust me, I think its bogus we call score() twice: but if something is put in
rather quickly on this issue (e.g. more caching) then i prefer if its more
contained so it can easily be ripped out later, when the problem is ultimately
solved correctly.
> 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
> Assignee: David Smiley
> Attachments: LUCENE-4574.patch, LUCENE-4574.patch, 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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