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) } ```