[LUCENE-10660] precompute the max level in LogMergePolicy

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 9.2
• Fix Version/s: 9.4
• Component/s: core/index
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: tang donghai
• Created: 24/Jul/22 05:39
• Updated: 28/Aug/22 16:43
• Resolved: 26/Jul/22 11:44

Description

I notice LogMergePolicy#findMerges will always calculate  max level on the right side when find the next segments to merge.

 

I think we could calculate the max levels only once, and when we need the max level, we could simply

float maxLevel = maxLevels[start];

and the precomputed code looks like below, compare each level in levels from right to left

float[] maxLevels = new float[numMergeableSegments + 1];
maxLevels[numMergeableSegments] = -1.0f;
for (int i = numMergeableSegments - 1; i >= 0; i--) {
      maxLevels[i] = Math.max(levels.get(i).level, maxLevels[i + 1]);
}

 

Issue Links

• links to: GitHub Pull Request #1045