[jira] [Closed] (LUCENE-7421) Speed up BS2 by caching the 2nd lowest doc id in the priority queue

["Adrien Grand (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LUCENE-7421?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Adrien Grand closed LUCENE-7421.
--------------------------------
    Resolution: Won't Fix

Hmm actually it helps less (only 2-3%) when the boolean query is nested under a conjunction (which is typically how BS2 gets used), so this is probably not that interesting.

{noformat}
         AndMedOrHighLow       22.62      (2.3%)       23.24      (2.3%)    2.7% (  -1% -    7%)
{noformat}

> Speed up BS2 by caching the 2nd lowest doc id in the priority queue
> -------------------------------------------------------------------
>
>                 Key: LUCENE-7421
>                 URL: https://issues.apache.org/jira/browse/LUCENE-7421
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Adrien Grand
>            Assignee: Adrien Grand
>            Priority: Minor
>         Attachments: LUCENE-7421.patch
>
>
> BS2 uses a priority queue in order to merge several sorted iterators into a new sorted iterator. We call updateTop every time that we move the 'top' iterator forward, which requires to check the size of the priority queue at least twice and perform at least two comparisons of doc ids.
> Instead, DisjunctionSumScorer could cache the 2nd lowest doc id of the priority queue and only call updateTop when the doc id of the entry at the top of the priority queue goes beyong the 2nd lowest doc id. While this would involve slightly more work in the case that the PQ has two high-cardinality clauses whose docs are interleaved, this would help when one clause has a much higher cardinality than the other ones or when the doc ids of the various clauses are clustered.



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