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https://issues.apache.org/jira/browse/LUCENE-8681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16769854#comment-16769854
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Mike Sokolov commented on LUCENE-8681:
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bq. ... doMaxScore and trackTotalHits (did you mean totalHitsThreshold?) aren't
parameters in master.
Oops - I was looking at an old branch; yes it's much cleaner now. Although
there's some javadoc still hanging around referring to doMaxScore.
I'll add the new static createManager with a test soon. I could clean up the
IndexSearcher javadocs here too, although it's not really related, it seems
pretty trivial.
I think I see your point about the enum - it's unusual to want to set a
specific value for these things. Maybe you'd set totalHitsThreshold to be some
multiple of numHits? But that could certainly remain an expert API, while
exposing the ability to either use the default (1000) or insist on precise
counts. I don't know if people are missing that ability or not.
> Prorated early termination
> --------------------------
>
> Key: LUCENE-8681
> URL: https://issues.apache.org/jira/browse/LUCENE-8681
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/search
> Reporter: Mike Sokolov
> Priority: Major
>
> In this issue we'll exploit the distribution of top K documents among
> segments to extract performance gains when using early termination. The basic
> idea is we do not need to collect K documents from every segment and then
> merge. Rather we can collect a number of documents that is proportional to
> the segment's size plus an error bound derived from the combinatorics seen as
> a (multinomial) probability distribution.
> https://github.com/apache/lucene-solr/pull/564 has the proposed change.
> [~rcmuir] pointed out on the mailing list that this patch confounds two
> settings: (1) whether to collect all hits, ensuring correct hit counts, and
> (2) whether to guarantee that the top K hits are precisely the top K.
> The current patch treats this as the same thing. It takes the position that
> if the user says it's OK to have approximate counts, then it's also OK to
> introduce some small chance of ranking error; occasionally some of the top K
> we return may draw from the top K + epsilon.
> Instead we could provide some additional knobs to the user. Currently the
> public API is {{TopFieldCOllector.create(Sort, int, FieldDoc, int
> threshold)}}. The threshold parameter controls when to apply early
> termination; it allows the collector to terminate once the given number of
> documents have been collected.
> Instead of using the same threshold to control leaf-level early termination,
> we could provide an additional leaf-level parameter. For example, this could
> be a scale factor on the error bound, eg a number of standard deviations to
> apply. The patch uses 3, but a much more conservative bound would be 4 or
> even 5. With these values, some speedup would still result, but with a much
> lower level of ranking errors. A value of MAX_INT would ensure no leaf-level
> termination would ever occur.
> We could also hide the precise numerical bound and offer users a three-way
> enum (EXACT, APPROXIMATE_COUNT, APPROXIMATE_RANK) that controls whether to
> apply this optimization, using some predetermined error bound.
> I posted the patch without any user-level tuning since I think the user has
> already indicated a preference for speed over precision by specifying a
> finite (global) threshold, but if we want to provide finer control, these two
> options seem to make the most sense to me. Providing access to the number of
> standard deviation to allow from the expected distribution gives the user the
> finest control, but it could be hard to explain its proper use.
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