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https://issues.apache.org/jira/browse/LUCENE-1506?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12668244#action_12668244
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John Wang commented on LUCENE-1506:
-----------------------------------
Filter calculates a DocSet given an IndexReader. Imagine a large index, and the
logic to calculate whether it is in the set is non-trivial, so building this
DocSet can be expensive.
So in the case where the driving query produces a very small result set, the
validation can be performed only on the small set via the match call.
Yes, in terms of functionality, one can do this with a filter, but it is
wasteful to perform the validation calculation on the entire index where the
candidates to be in the hits set is small.
> Adding FilteredDocIdSet and FilteredDocIdSetIterator
> ----------------------------------------------------
>
> Key: LUCENE-1506
> URL: https://issues.apache.org/jira/browse/LUCENE-1506
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Affects Versions: 2.4
> Reporter: John Wang
> Attachments: filteredDocidset.txt
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> Adding 2 convenience classes: FilteredDocIdSet and FilteredDocIDSetIterator.
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