[IMPALA-9915] Num distinct values for IS [NOT] NULL predicate should be 2

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: Impala 3.4.0
• Component/s: Frontend
• Epic Color: ghx-label-3
• Assignee: Unassigned
• Reporter: Aman Sinha
• Created: 02/Jul/20 05:51
• Updated: 02/Jul/20 06:02

Description

Currently, the NDV of all predicates is hardcoded to 3 following the 3-valued logic (True/False/Unknown). This is done in Predicate.analyzeImpl() method. For IsNullPredicate which represents IS NULL and IS NOT NULL, strictly speaking the NDV should be 2 since it should only evaluate to True or False. Fixing this is more of a technicality and probably won't affect explain plans in the tests. There are targeted tests in ExprCardinalityTest that should be updated when this is fixed.