pingcap/tidb

The heavy predicates may not need to be pushed down.

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#14,608 opened on Feb 3, 2020

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help wantedsig/plannertype/enhancement

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Description

For example, a big CASE...WHEN... clause may consume a lot of resources. In this case, push it down to table side may be worse than not pushing it.

We should control its behavior by

  • A hint to disable all predicates of one WHERE clause.
  • A cost-based or a heuristic method to control the predicates automatically.

Contributor guide

Research direction
Examine the predicate pushdown logic in TiDB's optimizer to determine when heavy predicates like CASE...WHEN should not be pushed down. Propose a cost based or heuristic method to control the behavior.
Tech stack
go
Domain
backenddatabaseperformance
Issue type
Performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
GoSQL
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40