[LUCENE-7020] TieredMergePolicy - cascade maxMergeAtOnce setting to maxMergeAtOnceExplicit

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 5.4.1
• Fix Version/s: 8.10
• Lucene Fields: New
• Assignee: Shawn Heisey
• Reporter: Shawn Heisey
• Created: 10/Feb/16 06:40
• Updated: 28/Aug/22 14:49
• Resolved: 24/Aug/21 08:57

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.

Issue Links

• links to: GitHub Pull Request #230