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From "Ryan Ernst (JIRA)" <>
Subject [jira] [Commented] (LUCENE-5527) Make the Collector API work per-segment
Date Thu, 03 Apr 2014 17:13:15 GMT


Ryan Ernst commented on LUCENE-5527:

I guess I wish AtomicReader were named LeafReader.
So maybe we shouldnt try to tackle that on this issue.
I agree 'atomic' is a bad name.  Why not name this LeafCollector now, since it makes more
sense on its own?

> Make the Collector API work per-segment
> ---------------------------------------
>                 Key: LUCENE-5527
>                 URL:
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Adrien Grand
>            Priority: Minor
>             Fix For: 5.0
>         Attachments: LUCENE-5527.patch
> Spin-off of LUCENE-5299.
> LUCENE-5229 proposes different changes, some of them being controversial, but there is
one of them that I really really like that consists in refactoring the {{Collector}} API in
order to have a different Collector per segment.
> The idea is, instead of having a single Collector object that needs to be able to take
care of all segments, to have a top-level Collector:
> {code}
> public interface Collector {
>   AtomicCollector setNextReader(AtomicReaderContext context) throws IOException;
> }
> {code}
> and a per-AtomicReaderContext collector:
> {code}
> public interface AtomicCollector {
>   void setScorer(Scorer scorer) throws IOException;
>   void collect(int doc) throws IOException;
>   boolean acceptsDocsOutOfOrder();
> }
> {code}
> I think it makes the API clearer since it is now obious {{setScorer}} and {{acceptDocsOutOfOrder}}
need to be called after {{setNextReader}} which is otherwise unclear.
> It also makes things more flexible. For example, a collector could much more easily decide
to use different strategies on different segments. In particular, it makes the early-termination
collector much cleaner since it can return different atomic collectors implementations depending
on whether the current segment is sorted or not.
> Even if we have lots of collectors all over the place, we could make it easier to migrate
by having a Collector that would implement both Collector and AtomicCollector, return {{this}}
in setNextReader and make current concrete Collector implementations extend this class instead
of directly extending Collector.

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