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Posted to issues@lucene.apache.org by "David Smiley (Jira)" <ji...@apache.org> on 2022/03/03 14:43:00 UTC
[jira] [Updated] (LUCENE-10302) PriorityQueue: optimize where we collect then iterate by using O(N) heapify
[ https://issues.apache.org/jira/browse/LUCENE-10302?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
David Smiley updated LUCENE-10302:
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Attachment: LUCENE_PriorityQueue_Builder_with_heapify.patch
> PriorityQueue: optimize where we collect then iterate by using O(N) heapify
> ---------------------------------------------------------------------------
>
> Key: LUCENE-10302
> URL: https://issues.apache.org/jira/browse/LUCENE-10302
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: David Smiley
> Priority: Major
> Attachments: LUCENE_PriorityQueue_Builder_with_heapify.patch
>
>
> Looking at LUCENE-8875 (LargeNumHitsTopDocsCollector.java ) I got to wondering if there was faster-than O(N*log(N)) way of loading a PriorityQueue when we provide a bulk array to initialize the heap/PriorityQueue. It turns out there is: the JDK's PriorityQueue supports this in its constructors, referring to "This classic algorithm due to Floyd (1964) is known to be O(size)" -- heapify() method. There's [another|https://www.geeksforgeeks.org/building-heap-from-array/] that may or may not be the same; I didn't look too closely yet. I see a number of uses of Lucene's PriorityQueue that first collects values and only after collecting want to do something with the results (typical / unsurprising). This lends itself to a builder pattern that can look similar to LargeNumHitsTopDocsCollector in terms of first having an array used like a list and then move over to the PriorityQueue if/when it gets full (it may not).
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