pingcap/tidb

use monotonic time directly instead of Go time in somewhere

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#32,121 opened on Feb 7, 2022

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help wantedtype/enhancementtype/performance

Description

Enhancement

In TiDB, we heavily use Go time.Now to calculate the duration of some operations, e.g. prometheus Histogram, query time, etc.

For time.Now, this function will call walltime and nanotime, but in the above scenario, we only need to call nanotime(monotonic clock) to calculate the duration.

import _ "unsafe"
//go:noescape
//go:linkname nanotime runtime.nanotime
func nanotime() int64

func Now() time.Duration {
	return time.Duration(nanotime())
}

Here is a simple implementation for Nanotime,


func BenchmarkTime1(b *testing.B) {
	for i := 0; i < b.N; i++ {
		time.Now()
	}
}

func BenchmarkTime2(b *testing.B) {
	for i := 0; i < b.N; i++ {
		Now()
	}
}

The benchmark result is:

BenchmarkTime1-8          	17705235	        65.90 ns/op
BenchmarkTime2-8          	38601799	        29.68 ns/op

Contributor guide

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.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Go basicsGo time packageprofiling
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Identify all places in TiDB source code where time.Now is used to calculate durations (e.g., Prometheus Histogram, query time). Replace with a function that uses runtime.nanotime directly, as shown in the issue. Review the provided benchmark results to validate improvement. Check existing comments for suggested areas or concerns.