[CALCITE-3546] Improve EnumerableDefaults nested loop join

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 1.21.0
• Fix Version/s: 1.22.0
• Labels: pull-request-available
• Assignee: Ruben Q L
• Reporter: Ruben Q L
• Created: 28/Nov/19 19:15
• Updated: 06/Mar/20 07:35
• Resolved: 05/Dec/19 11:14

Description

The current implementation of EnumerableDefaults#nestedLoopJoin builds the complete join result in a list before returning it. As specified in a comment there, this is "easy, but hogs memory". Also, it is not very efficient if after the join there is a LIMIT.
An alternative implementation of nested loop join can be proposed, based on iterating through the outer an inner enumerables, and returning the results step by step (something similar to EnumerableDefaults#correlateJoin).

Issue Links

• blocks: CALCITE-3535 EnumerableJoinRule: remove unnecessary Filter on top of INNER Join
• links to: GitHub Pull Request #1614