[CALCITE-2883] HepPlanner subprogram may loop till getting out of memory

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Invalid
• Labels: pull-request-available
• Assignee: Jesús Camacho Rodríguez
• Reporter: Jesús Camacho Rodríguez
• Created: 01/Mar/19 00:44
• Updated: 27/Feb/24 22:23
• Resolved: 01/Mar/19 21:23

Description

Consider the following two hep programs.

Program 1:

final HepProgramBuilder programBuilder = new HepProgramBuilder();
programBuilder.addMatchOrder(HepMatchOrder.BOTTOM_UP);
programBuilder.addRuleInstance(JoinToMultiJoinRule.INSTANCE);
programBuilder.addRuleInstance(LoptOptimizeJoinRule.INSTANCE);
final HepProgram program = programBuilder.build();

Program 2:

final HepProgramBuilder programBuilder = new HepProgramBuilder();
final HepProgramBuilder subprogramBuilder = new HepProgramBuilder();
subprogramBuilder.addMatchOrder(HepMatchOrder.BOTTOM_UP);
subprogramBuilder.addRuleInstance(JoinToMultiJoinRule.INSTANCE);
subprogramBuilder.addRuleInstance(LoptOptimizeJoinRule.INSTANCE);
programBuilder.addSubprogram(subprogramBuilder.build());
final HepProgram program = programBuilder.build();

I would expect both programs to behave similarly. However, program 2 will loop indefinitely. The reason is that HepPlanner subprogram execution loops if subprogram generates any new expression.
https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/plan/hep/HepPlanner.java#L339
This does not seem right since planner can control exiting the program (and thus, subprogram) depending on its own internal state and configuration properties, e.g., match limit.

Issue Links

• is related to: HIVE-21365 Refactor Hep planner steps in CBO
• links to: GitHub Pull Request #1079