t.go

package main

import (
        "context"
        "database/sql"
        _ "github.com/go-sql-driver/mysql"
        "log"
        "sync"
        "time"
)

func main() {
        db, _ := sql.Open("mysql", "root@tcp(127.0.0.1:3306)/")

        var waitTimeout int
        err := db.QueryRow("SELECT @@wait_timeout").Scan(&waitTimeout)
        if err != nil {
                panic(err)
        }
        log.Printf("wait_timeout=%v", waitTimeout)

        var wg sync.WaitGroup

        for i := 60; i < 3600; i += 30 {
                c, err := db.Conn(context.Background())
                if err != nil {
                        log.Print(err)
                        break
                }
                wg.Add(1)
                go func(c *sql.Conn, n int) {
                        time.Sleep(time.Second * time.Duration(n))
                        _, err := c.ExecContext(context.Background(), "SELECT 42")
                        log.Printf("%v - %v", n, err)
                        c.Close()
                        wg.Done()
                }(c, i)
        }
        wg.Wait()
}