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https://issues.apache.org/jira/browse/LUCENE-8688?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16793486#comment-16793486
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ASF subversion and git services commented on LUCENE-8688:
---------------------------------------------------------

Commit 425f207f4098e4fcc1307729b1f2e17cfef3929f in lucene-solr's branch 
refs/heads/master from Adrien Grand
[ https://gitbox.apache.org/repos/asf?p=lucene-solr.git;h=425f207 ]

LUCENE-8688: Forced merges merge more than necessary.


> Forced merges merge more than necessary
> ---------------------------------------
>
>                 Key: LUCENE-8688
>                 URL: https://issues.apache.org/jira/browse/LUCENE-8688
>             Project: Lucene - Core
>          Issue Type: Bug
>            Reporter: Adrien Grand
>            Priority: Minor
>         Attachments: LUCENE-8688.patch, LUCENE-8688.patch, LUCENE-8688.patch, 
> LUCENE-8688.patch
>
>
> A user reported some surprise after the upgrade to Lucene 7.5 due to changes 
> to how forced merges are selected when maxSegmentCount is greater than 1.
> Before 7.5 forceMerge used to pick up the least amount of merging that would 
> result in an index that has maxSegmentCount segments at most. Now that we 
> share the same logic as regular merges, we are almost sure to pick a 
> maxMergeAtOnceExplicit-segments merge (30 segments) given that merges that 
> have more segments usually score better. This is due to the fact that natural 
> merges assume that merges that run now save work for later, so the more 
> segments get merged, the better. This assumption doesn't hold for forced 
> merges that should run on read-only indices, so there won't be any future 
> merging.



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