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From "Shai Erera (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-1614) Add next() and skipTo() variants to DocIdSetIterator that return the current doc, instead of boolean
Date Thu, 30 Apr 2009 08:05:30 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-1614?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12704522#action_12704522
] 

Shai Erera commented on LUCENE-1614:
------------------------------------

I think I understand what you mean, but please correct me if I'm wrong. You propose this check()
so that in case a DISI can save any extra operations it does in next() (such as reading a
payload for example) it will do so. Therefore in the example you give above with CS, next()'s
contract forces it to advance all the sub-scorers, but with check() it could stop in the middle.

This warrants an explicit documentation and implementation by current DISIs ... I don't think
that if you call a DISI today with next(10) and next(10) it will not move to 11 in the second
call. But calling check(10) and next(10) MUST not advance the DISI further than 10. If the
default impl in DISI just uses nextDoc() and returns true if the return value is the requested,
we should be safe back-compat-wise, but this is still dangerous and we need clear documentation.

BTW, perhaps a testAndSet-like version can save check(10) followed by a next(10), and will
fit nicer?

> 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
>
>
> 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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