[CALCITE-3178] RexSimplify.simplifyOrTerms slow with large OR filters

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.19.0
• Assignee: Unassigned
• Reporter: Gian Merlino
• Created: 07/Jul/19 15:49
• Updated: 15/Jul/19 19:42

Description

In particular, once for each subpredicate within the OR, RexSimplify.simplifyOrTerms calls simplify.predicates.union and adds the freshly-unioned result to simplify.predicates. The most time-consuming part of this seems to be RexUtil.predicateConstants, which re-examines each previously-added entry. This is O(N^2) in the number of subpredicates within the OR.

I discovered this when someone tried to run a query with a 14,000-element IN filter, and planning took about 45 seconds. In Druid, we always convert INs to ORs, never allowing Calcite's subquery conversion to happen. This is because as far as native Druid queries are concerned, a huge OR is going to be more efficient than a join against a constant subquery.

I'm not sure what the best way is to fix this. The only thing that comes to mind immediately is the "quick fix" of limiting how many OR elements RexSimplify might attempt to simplify at once (and potentially AND as well? I haven't looked into that one.)

Issue Links

• relates to: CALCITE-2449 RexSimplify overhaul