pingcap/tidb

Show the spill to disk cost for Sort operator

Open

#25,850 opened on Jun 30, 2021

View on GitHub
 (2 comments) (0 reactions) (2 assignees)Go (6,186 forks)batch import
good first issuesig/executiontype/enhancement

Repository metrics

Stars
 (40,090 stars)
PR merge metrics
 (Avg merge 14d 4h) (346 merged PRs in 30d)

Description

Enhancement

Note that I'm not sure whether the explain analyze can get the spill cost of other operators.

For sort, if no spill to disk triggered, most of its cost is the memory sort. So we might not need to record the detailed cost in explain analyze. But the cost of it would be split into two parts if the spill is triggered. It first spills all things to disk. Then perform k-way merge and returning data row by row. It would be useful for investigating the actual cost part if we can record both of them or just the spill cost in EXPLAIN ANALYZE

Contributor guide

Research direction
Study the Sort operator implementation in TiDB's executor package, understand how EXPLAIN ANALYZE collects execution costs, and identify where spill to disk cost is incurred. Then design a way to expose that cost separately.
Tech stack
go
Domain
backend
Issue type
Feature
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.
1-2 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
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50