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https://issues.apache.org/jira/browse/LUCENE-10576?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17538321#comment-17538321
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Chris M. Hostetter commented on LUCENE-10576:
---------------------------------------------
Should those "reasonable items" be added as comments to the code so they aren't
lost to time?
> ConcurrentMergeScheduler maxThreadCount calculation is artificially low
> -----------------------------------------------------------------------
>
> Key: LUCENE-10576
> URL: https://issues.apache.org/jira/browse/LUCENE-10576
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Kevin Risden
> Assignee: Kevin Risden
> Priority: Minor
> Time Spent: 1h 40m
> Remaining Estimate: 0h
>
> [https://github.com/apache/lucene/blob/main/lucene/core/src/java/org/apache/lucene/index/ConcurrentMergeScheduler.java#L177]
> {code:java}
> maxThreadCount = Math.max(1, Math.min(4, coreCount / 2));
> {code}
> This has a practical limit of max of 4 threads due to the Math.min. This
> doesn't take into account higher coreCount.
> I can't seem to tell if this is by design or this is just a mix up of logic
> during the calculation.
> If I understand it looks like 1 and 4 are mixed up and should instead be:
> {code:java}
> maxThreadCount = Math.max(4, Math.min(1, coreCount / 2));
> {code}
> which then simplifies to
> {code:java}
> maxThreadCount = Math.max(4, coreCount / 2);
> {code}
> So that you have a minimum of 4 maxThreadCount and max of coreCount/2.
> ----
> Based on the history I could find, this has been this way forever.
> * LUCENE-6437
> * LUCENE-6119
> * LUCENE-5951
> ** Introduced as "maxThreadCount = Math.max(1, Math.min(3,
> Runtime.getRuntime().availableProcessors()/2));"
> **
> https://github.com/apache/lucene/commit/33410e30c1af7105a6b8b922255af047d13be626#diff-ceb8ec6fe5807682cfb691a8ec52bcc672fb7c5eeb6922c80da4c075f7f003c8R147
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