[CALCITE-4578] redundant HepPlanner#buildFinalPlan when there's no rule fired in the program

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: core
• Assignee: Jiatao Tao
• Reporter: Jiatao Tao
• Created: 11/Apr/21 09:37
• Updated: 22/Apr/21 02:38

Description

Example like that: insert xxx VALUES (1, 'one'), (2, 'two'), (3, 'three')...(10000, 'ten thousand');

It generates a Union node with 10000 inputs, and the performance is poor, here's the profile:

We create a program(HepProgram) to do the union merge, in this case, we only have one union, so the rule is not fired, but it will still build the buildFinalPlan, and AbstractRelNode#explain has performance issue in this case(see the flame graph):

public RelNode findBestExp() {
  assert root != null;

  executeProgram(mainProgram);

  // Get rid of everything except what's in the final plan.
  collectGarbage();

  return buildFinalPlan(root);
}

And the union has large inputs, so the performance is poor(in SetOp#replaceInput, we have to recomputeDigest ), we can skip buildFinalPlan if there's no rule fired.