[CALCITE-4514] [CALCITE-4514] Fine tune the merge order of two RelSets

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 1.27.0
• Labels: pull-request-available
• Assignee: Unassigned
• Reporter: Botong Huang
• Created: 26/Feb/21 06:20
• Updated: 03/Jun/21 22:31
• Resolved: 28/Feb/21 21:11

Description

When merging two relsets, we have two preferences:
1. Merge parent relset into child relset
2. Merge newer relset into older relset
Currently, when the two relsets are parent set of each other, we randomly pick a merge order without checking the second condition above. For performance reasons, we should, to avoid unnecessary churn.

Issue Links

• links to: GitHub Pull Request #2358