[jira] [Resolved] (LUCENE-8393) TieredMergePolicy needs to take into account the maximum segment size when computing the allowed number of segments

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

     [ https://issues.apache.org/jira/browse/LUCENE-8393?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Adrien Grand resolved LUCENE-8393.
----------------------------------
       Resolution: Fixed
    Fix Version/s: 7.5
                   master (8.0)

> TieredMergePolicy needs to take into account the maximum segment size when computing the allowed number of segments
> -------------------------------------------------------------------------------------------------------------------
>
>                 Key: LUCENE-8393
>                 URL: https://issues.apache.org/jira/browse/LUCENE-8393
>             Project: Lucene - Core
>          Issue Type: Bug
>            Reporter: Adrien Grand
>            Priority: Minor
>             Fix For: master (8.0), 7.5
>
>         Attachments: LUCENE-8393.patch
>
>
> This is a pre-existing issue that was made more likely by LUCENE-7976, given that segments that are larger than the max segment size divided by 2 now are potential candidates for merging: when computing the allowed number of segments, TieredMergePolicy multiplies the level size by {{maxMergeAtOnce}} until it finds a level that isn't full. It currently assumes that the level size is always less than the maximum segment size, which might not always be true. This might lead to underestimating the allowed number of segments and in-turn causing excessive merging.



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