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https://issues.apache.org/jira/browse/LUCENE-5527?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13958891#comment-13958891
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Adrien Grand commented on LUCENE-5527:
--------------------------------------

I chose these names to make it clear what these classes relate to:
 - IndexReader -> Collector
 - AtomicReader -> AtomicCollector

But I'm totally open to better names!

> Make the Collector API work per-segment
> ---------------------------------------
>
>                 Key: LUCENE-5527
>                 URL: https://issues.apache.org/jira/browse/LUCENE-5527
>             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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