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https://issues.apache.org/jira/browse/LUCENE-1849?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12747637#action_12747637
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Michael McCandless commented on LUCENE-1849:
--------------------------------------------

bq. Any stats on the performance gains here available?

I think somewhere in LUCENE-1483 is the answer to this question, but I can't 
find it now.  (We need a whole new search index just for that issue alone!).  
But the optimization currently only applies if the query contains just SHOULD 
terms plus up to 32 MUST_NOT terms.  More testing here would be great... the 
specialized search in LUCENE-1594 also uses out-of-order collection for certain 
AND queries but I haven't confirmed if/when that's a win.

{quote}
Also, are the implications of out of order docids coming back from nextDoc() 
well documented (javadoc?, wiki?)?
I guess out of order docids really screw up advance(int), so you should never 
call advance(int) if you allowed out of order collection for a Scorer?
{quote}

Out-of-order scoring is only used for top-scorers today in Lucene, so 
nextDoc/advance are not used.  (Though: BooleanScorer, which provides docs 
out-of-order, is I think able to nextDoc() through the out-of-order docs, but I 
don't think we take advantage of that anywhere, though we could do so to 
improve performance of BooleanQuery as a sub-clause of BooleanQuery).

> Add OutOfOrderCollector and InOrderCollector subclasses of Collector
> --------------------------------------------------------------------
>
>                 Key: LUCENE-1849
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1849
>             Project: Lucene - Java
>          Issue Type: Wish
>          Components: Search
>    Affects Versions: 2.9
>            Reporter: Tim Smith
>            Priority: Minor
>             Fix For: 2.9
>
>
> I find myself always having to implement these methods, and i always return a 
> constant (depending on if the collector can handle out of order hits)
> would be nice for these two convenience abstract classes to exist that 
> implemented acceptsDocsOutOfOrder() as final and returned the appropriate 
> value

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