txrace.go

package main

import (
	"context"
	"database/sql"
	"fmt"
	"log"
	"os"
	"time"

	_ "github.com/go-sql-driver/mysql"
)

func main() {
	if len(os.Args) != 2 {
		log.Fatalf("usage: %s <dbname>", os.Args[0])
	}
	dbName := os.Args[1]
	db, err := sql.Open("mysql", "root@/"+dbName)
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	db.SetMaxOpenConns(100)
	db.SetMaxIdleConns(100)

	if _, err := db.Exec("drop table if exists t"); err != nil {
		log.Fatal(err)
	}
	if _, err := db.Exec("create table t (id int not null auto_increment primary key)"); err != nil {
		log.Fatal(err)
	}

	ins, err := db.Prepare("insert into t (id) values (null)")
	if err != nil {
		log.Fatal(err)
	}

	sel, err := db.Prepare("select count(*) from t")
	if err != nil {
		log.Fatal(err)
	}

	for i := 0; i < 10; i++ {
		go func() {
			for i := 0; ; i++ {
				runTx(db, ins)
			}
		}()
	}
	for range time.Tick(time.Second) {
		var n int
		r := sel.QueryRow()
		if err := r.Scan(&n); err != nil {
			fmt.Println("select", err)
			continue
		}
		fmt.Printf("%d rows (should be 0)\n", n)
	}
}

func runTx(db *sql.DB, stmt *sql.Stmt) error {
	ctx, cancel := context.WithCancel(context.Background())
	quit := make(chan struct{})
	done := make(chan struct{})
	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		fmt.Println("begin", err)
		return err
	}
	defer tx.Rollback()

	stmt = tx.Stmt(stmt)

	go func() {
		timer := time.NewTimer(time.Microsecond)
		defer timer.Stop()
		select {
		case <-quit:
		case <-timer.C:
		}
		cancel()
		close(done)
	}()
	defer func() {
		close(quit)
		<-done
	}()

	for i := 0; i < 10; i++ {
		if _, err := stmt.Exec(); err != nil {
			return err
		}
	}
	_ = tx.Rollback()
	return nil
}