[IMPALA-8022] Add cardinality checks to PlannerTest

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: Impala 3.1.0
• Component/s: Frontend
• Epic Color: ghx-label-4
• Assignee: Paul Rogers
• Reporter: Paul Rogers
• Created: 28/Dec/18 01:12
• Updated: 30/Jan/19 23:06
• Resolved: 30/Jan/19 23:06

Description

IMPALA-8021 suggests that we add cardinality to the standard EXPLAIN output. When we do so, the cardinality will appear in the plans generated by PlannerTest. We could just ignore the numbers, as we do for other derived values. Or, we could use this opportunity to verify the expected cardinalities.

The expected cardinality is a critical number when planning queries: we decide join planning based on that number (sometimes multiplied by row width.) To prevent regressions, we want to verify that we've not changed the cardinality estimates except by design.

Since cardinality estimates may vary a bit, do a range-based comparison, accepting as valid any value within 5% of the expected value. (Except for zero, if zero is expected, the actual estimate must also be zero.)

Issue Links

• is part of: IMPALA-8021 Add estimated cardinality to EXPLAIN output