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https://issues.apache.org/jira/browse/LUCENE-10207?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17441817#comment-17441817
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Greg Miller commented on LUCENE-10207:
--------------------------------------
OK, I buy that. I hadn't spent enough time looking at how [disjunction cost is
estimated|https://github.com/apache/lucene/blob/main/lucene/core/src/java/org/apache/lucene/search/ScorerUtil.java#L25],
but after looking into that logic, I agree this should be consistent with a
disjunction where minShouldMatch is effectively 1.
So I think that just looks like the following (with the proposal that MTQ can
provide its number of unique terms, or -1 if it doesn't know up-front):
{code:java}
final long cost;
final int queryTermsCount = query.getTermsCount();
if (queryTermsCount == -1) {
cost = indexTerms.getSumDocFreq();
} else {
cost = queryTermsCount + (indexTerms.getSumDocFreq() -
indexTerms.size());
}
{code}
> Make TermInSetQuery usable with IndexOrDocValuesQuery
> -----------------------------------------------------
>
> Key: LUCENE-10207
> URL: https://issues.apache.org/jira/browse/LUCENE-10207
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Adrien Grand
> Priority: Minor
> Attachments: LUCENE-10207_multitermquery.patch
>
>
> IndexOrDocValuesQuery is very useful to pick the right execution mode for a
> query depending on other bits of the query tree.
> We would like to be able to use it to optimize execution of TermInSetQuery.
> However IndexOrDocValuesQuery only works well if the "index" query can give
> an estimation of the cost of the query without doing anything expensive (like
> looking up all terms of the TermInSetQuery in the terms dict). Maybe we could
> implement it for primary keys (terms.size() == sumDocFreq) by returning the
> number of terms of the query? Another idea is to multiply the number of terms
> by the average postings length, though this could be dangerous if the field
> has a zipfian distribution and some terms have a much higher doc frequency
> than the average.
> [~romseygeek] and I were discussing this a few weeks ago, and more recently
> [~mikemccand] and [~gsmiller] again independently. So it looks like there is
> interest in this. Here is an email thread where this was recently discussed:
> https://lists.apache.org/thread.html/re3b20a486c9a4e66b2ca4a2646e2d3be48535a90cdd95911a8445183%40%3Cdev.lucene.apache.org%3E.
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