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https://issues.apache.org/jira/browse/SOLR-12407?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16512146#comment-16512146
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Alan Woodward commented on SOLR-12407:
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I'd missed this, sorry for not picking it up earlier.
It looks as though BoostedQuery just assumed that all docs had a value, so
avoided the exists check. I'm not entirely sure that's a safe assumption, but
from looking at a few ValueSource implementations it does seem that they have
default return values and so the exists check isn't actually necessary. So the
best solution is I think to remove the exists call from
ValueSource.WrappedDoubleValuesSource and always return true from advanceExact()
> edismax boost performance regression from switch to FunctionScoreQuery
> ----------------------------------------------------------------------
>
> Key: SOLR-12407
> URL: https://issues.apache.org/jira/browse/SOLR-12407
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Affects Versions: 7.3
> Reporter: Will Currie
> Priority: Minor
> Attachments: restore-boosted-query.patch, solr-7.2.svg, solr-7.3.svg
>
>
> Assertion: FunctionScoreQuery uses the iterator style API (advanceExact +
> doubleValue). BoostedQuery uses the "old" api (just a single call to
> doubleValue). In an edismax boost this means the boost function is called
> twice for every document being scored in 7.3 instead of once in 7.2.
> I'm seeing ~50% increase in query response time after upgrading from 7.2 to
> 7.3 (600ms to 900ms). My queries use an edismax boost something like:
> {noformat}
> if(termfreq(type,"A"),product(map(field1,3,3,1.5,1),map(field1,4,4,1.9,1),if(def(field2,false),product(map(field1,1,1,0.6,1),map(field1,2,2,0.7,1),if(not(exists(field1)),0.6,1),map(field3,0,0,1.3,1)),product(map(field1,1,1,0.7,1),map(field1,2,2,1.1,1),if(not(exists(field1)),0.90,1),map(field3,0,0,1.50,1)))),1){noformat}
> This boost is likely (surely?) suboptimal but LUCENE-8099 appears to have
> introduced this performance regression (poured proverbial oil on my
> smouldering fire). If I change ExtendedDismaxQParser back to using the
> deprecated BoostedQuery I get the 600ms solr 7.2 response time back.
> It appears FunctionScoreQuery invokes the boost function twice for each
> document. Once with a call to
> [exists()|https://github.com/apache/lucene-solr/blob/03afeb7766a39996de3c85e8a6ab24d2a352dd1c/lucene/queries/src/java/org/apache/lucene/queries/function/ValueSource.java#L150]
> from
> [advanceExact()|https://github.com/apache/lucene-solr/blob/42154387d4f2a6060da09c4236e2a8dbb575c59e/lucene/queries/src/java/org/apache/lucene/queries/function/FunctionScoreQuery.java#L170],
> then a second time from the call chain following scores.doubleValue().
> I don't know if that's the cause of the slowdown but I'm definitely seeing a
> slowdown that disappears when I revert part of LUCENE-8099.
> I've attached some flamegraphs comparing 7.2 and 7.3. The frame
> FunctionScoreQuery$FunctionScoreWeight$1.score in solr-7.3.svg show 2
> "towers". One for advanceExact (calling exists()), the other for
> doubleValue() which ends up similar to solr-7.2.svg.
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