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https://issues.apache.org/jira/browse/LUCENE-2766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12977376#action_12977376
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Robert Muir commented on LUCENE-2766:
-------------------------------------
I'm gonna hold off on LUCENE-2771 until we figure this one out... because it
would make your getSequentialSubReaders in the synced=true case quite heavy
(without modifications).
This is because in that issue the norms caching is removed from the non-atomic
readers
(Dir/MultiReader) and pushed onto SlowMultiReaderWrapper/ParallelReader.
So one idea is to fix parallelreader to not 'sometimes' return
getSequentialSubReaders,
but instead have two supported approaches, one that supports the 'synced' case
properly with
per-segment search (and a suitable mergepolicy to go with it), another
(deprecated) one
to support the synced=false case?
Or reworded: is there any reason we shouldn't actually *only* support this way
going forwards
in the future?
> ParallelReader should support getSequentialSubReaders if possible
> -----------------------------------------------------------------
>
> Key: LUCENE-2766
> URL: https://issues.apache.org/jira/browse/LUCENE-2766
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Andrzej Bialecki
> Attachments: LUCENE-2766.patch
>
>
> Applications that need to use ParallelReader can't currently use per-segment
> optimizations because getSequentialSubReaders returns null.
> Considering the strict requirements on input indexes that ParallelReader
> already enforces it's usually the case that the additional indexes are built
> with the knowledge of the primary index, in order to keep the docId-s
> synchronized. If that's the case then it's conceivable that these indexes
> could be created with the same number of segments, which in turn would mean
> that their docId-s are synchronized on a per-segment level. ParallelReader
> should detect such cases, and in getSequentialSubReader it should return an
> array of ParallelReader-s created from corresponding segments of input
> indexes.
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