mysql 行锁

Read: ID=2, Value=999 Write: ID=1, NewValue=999 程序运行时间: 10.0269079s 为什么运行时间是10秒？读和写的不是同一条数据，mysql有行锁，写的时候锁住一行， 不影响其它行读取才对

package main

import (
    "fmt"
    "gorm.io/driver/mysql"
    "gorm.io/gorm"
    "gorm.io/gorm/clause"
    "log"
    "sync"
    "time"
)

// Data represents a data structure in the database.
type Data struct {
    ID    int
    Value int
}

var (
    dbMu sync.Mutex
    db   *gorm.DB
)

func initDB() {
    var err error
    dsn := "root:123456@tcp(localhost:3306)/demo?parseTime=true"
    db, err = gorm.Open(mysql.Open(dsn), &gorm.Config{})
    if err != nil {
        log.Fatal(err)
    }

    err = db.AutoMigrate(&Data{})
    if err != nil {
        log.Fatal(err)
    }
}

func main() {
    initDB()

    // Initialize the database with some data
    db.Create(&Data{ID: 1, Value: 100})
    db.Create(&Data{ID: 2, Value: 200})
    db.Create(&Data{ID: 3, Value: 300})

    startTime := time.Now()

    // Simulate concurrent read and write with row-level lock
    var wg sync.WaitGroup

    wg.Add(2)

    go func() {
        defer wg.Done()
        readData(2)
    }()

    go func() {
        defer wg.Done()
        writeData(1, 999)
    }()

    // 等待两个 goroutine 完成
    wg.Wait()

    endTime := time.Now()
    duration := endTime.Sub(startTime)
    fmt.Printf("程序运行时间: %s\n", duration)
}

func readData(id int) {
    dbMu.Lock()
    defer dbMu.Unlock()

    tx := db.Begin()
    defer tx.Rollback()

    var data Data

    // 使用 FOR UPDATE 子句对特定行加排他锁
    err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).First(&data, id).Error
    if err != nil {
        log.Fatal(err)
    }

    fmt.Printf("Read: ID=%d, Value=%d\n", data.ID, data.Value)

    // Simulate some processing time
    time.Sleep(time.Second * 5)

    tx.Commit()
}

func writeData(id, newValue int) {
    dbMu.Lock()
    defer dbMu.Unlock()

    tx := db.Begin()
    defer tx.Rollback()

    // 使用 FOR UPDATE 子句对特定行加排他锁
    err := tx.Model(&Data{}).Where("id = ?", id).Clauses(clause.Locking{Strength: "UPDATE"}).Update("value", newValue).Error
    if err != nil {
        log.Fatal(err)
    }

    fmt.Printf("Write: ID=%d, NewValue=%d\n", id, newValue)

    // 提交事务
    tx.Commit()

    // Simulate some processing time
    time.Sleep(time.Second * 5)
}