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https://issues.apache.org/jira/browse/LUCENE-1614?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12710851#action_12710851
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Michael McCandless commented on LUCENE-1614:
--------------------------------------------
{quote}
> This would save CPU for scorers that merge multiple sub-scorers (like
> BooleanScorer/2), because instead of having to check for -1 returned from
> each sub-scorer, they could simply proceed with their normal logic and check
> for Integer.MAX_VALUE just before collecting the doc.
But for scorers that use a priority queue, does checking and immediately
removing from the queue (hence making the heap smaller) offer any advantages? I
had assumed so since this is what current scorers do. Immediately removing
scorers also causes early termination for minimumNrMatchers>1 in
DisjunctionSumScorer.
{quote}
But that only helps at the tail end of the iteration, vs saving an if
check per-sub-scorer X per-next?
Ie presumably much more CPU is spent iterating while the PQ is full,
than while it's winding down, so saving the if per-sub-scorer-next is
better?
Also, I think over time we should migrate away from the PQ (ie, use
BooleanScorer's batch approach, not Disjunction*Scorer's PQ) since the
batch scoring approach gives better performance. EG I think we should
extend BooleanScorer to handle MUST clauses. BooleanScorer handles
doc=Integer.MAX_VALUE for a sub-scorer quite efficiently (the chunk is
always skipped for that sub-scorer, after one if check).
> Add next() and skipTo() variants to DocIdSetIterator that return the current
> doc, instead of boolean
> ----------------------------------------------------------------------------------------------------
>
> Key: LUCENE-1614
> URL: https://issues.apache.org/jira/browse/LUCENE-1614
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Reporter: Shai Erera
> Fix For: 2.9
>
> Attachments: LUCENE-1614.patch
>
>
> See
> http://www.nabble.com/Another-possible-optimization---now-in-DocIdSetIterator-p23223319.html
> for the full discussion. The basic idea is to add variants to those two
> methods that return the current doc they are at, to save successive calls to
> doc(). If there are no more docs, return -1. A summary of what was discussed
> so far:
> # Deprecate those two methods.
> # Add nextDoc() and skipToDoc(int) that return doc, with default impl in DISI
> (calls next() and skipTo() respectively, and will be changed to abstract in
> 3.0).
> #* I actually would like to propose an alternative to the names: advance()
> and advance(int) - the first advances by one, the second advances to target.
> # Wherever these are used, do something like '(doc = advance()) >= 0' instead
> of comparing to -1 for improved performance.
> I will post a patch shortly
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