pingcap/tidb

design vectorized aggregation functions

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#14,217 opened on Dec 25, 2019

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help wantedtype/enhancement

Description

Description

All our aggregation functions (in executor/aggfuncs/aggfuncs.go) used by the execution engine are row-based. We can vectorize them to improve their performance like what we do for all scalar functions.

Difficulty

  • Medium

Score

  • 3000

Mentor(s)

  • @SunRunAway
  • @XuHuaiyu
  • @qw4990

Recommended Skills

  • Go programming

Contributor guide

Tech stack
go
Domain
database
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.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Go programmingfamiliarity with TiDB executor
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
25
Research direction
Begin by studying the existing row based aggregation functions in executor/aggfuncs/aggfuncs.go to understand the current interface and logic. Look at already vectorized scalar functions (e.g., in expressions/scalar function) for patterns. Then design a vectorized version, possibly starting with a single aggregation function like sum or count. Consider performance implications and write benchmarks. No existing PRs or comments on this issue, so the design is open.