reduce optimizer cpu usage when handling very large IN(...) expression

Description

Contributor guide

Tech stack

gosql

Domain

backenddatabaseperformance

Issue type

performance

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

4

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

3-5 days

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

Go programmingunderstanding of SQL optimization

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

30

Research direction

Investigate the optimizer's handling of large IN(...) expressions in TiDB. Look at the expression evaluation and optimization code, likely in the planner package. The provided images show CPU profiling; identify where the bottleneck occurs. Consider approaches like early pruning or hash based evaluation. Check related issues or comments for suggested solutions.