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  1. Lucene - Core
  2. LUCENE-7020

TieredMergePolicy - cascade maxMergeAtOnce setting to maxMergeAtOnceExplicit

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Details

    • Improvement
    • Status: Closed
    • Major
    • Resolution: Fixed
    • 5.4.1
    • 8.10
    • None
    • None
    • New

    Description

      SOLR-8621 covers improvements in configuring a merge policy in Solr.

      Discussions on that issue brought up the fact that if large values are configured for maxMergeAtOnce and segmentsPerTier, but maxMergeAtOnceExplicit is not changed, then doing a forceMerge is likely to not work as expected.

      When I first configured maxMergeAtOnce and segmentsPerTier to 35 in Solr, I saw an optimize (forceMerge) fully rewrite most of the index twice in order to achieve a single segment, because there were approximately 80 segments in the index before the optimize, and maxMergeAtOnceExplicit defaults to 30. On advice given via the solr-user mailing list, I configured maxMergeAtOnceExplicit to 105 and have not had that problem since.

      I propose that setting maxMergeAtOnce should also set maxMergeAtOnceExplicit to three times the new value – unless the setMaxMergeAtOnceExplicit method has been invoked, indicating that the user wishes to set that value themselves.

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            elyograg Shawn Heisey
            elyograg Shawn Heisey
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