create index concurrently lead to block

[GMHDBJD]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

package main

import (
	"database/sql"
	"fmt"
	"os"
	"sync"
	"time"

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

var (
	cases = []string{
		"drop database if exists %s",
		"create database if not exists %s",
		"create table %s.t (id int)",
		"alter table %s.t add column col int", // no need, but will increase the probability of reproduction
		"alter table %s.t add index idx(id)",
	}
	wg sync.WaitGroup
)

func runSQL(dbName string, db *sql.DB) {
	defer wg.Done()

	for _, sqlFormat := range cases {
		sql := fmt.Sprintf(sqlFormat, dbName)
		fmt.Printf("run sql: %s\n", sql)
		_, err := db.Exec(sql)
		if err != nil {
			fmt.Printf("%v\n", err)
			os.Exit(2)
		}
	}
}

func main() {
	dsn := fmt.Sprintf("%s:%s@tcp(%s:%d)/",
		"root", "", "127.0.0.1", 4000)
	db, err := sql.Open("mysql", dsn)
	if err != nil {
		fmt.Printf("fail to open db")
		os.Exit(2)
	}
	if err := db.Ping(); err != nil {
		fmt.Printf("fail to ping db")
		os.Exit(2)
	}

	for i := 1; i <= 10; i++ {
		fmt.Printf("round %d\n", i)
		wg.Add(2)
		go runSQL("test_a", db)
		go runSQL("test_b", db)
		wg.Wait()
		time.Sleep(1 * time.Second)
	}
}

2. What did you expect to see? (Required)

success to execute alter table %s.t add index idx(id)

3. What did you see instead (Required)

the create index statement block

4. Affected version (Required)

v4.0.0-beta.2-737-g5f983b860

5. Root Cause Analysis

tidb log
debug-log.txt

[Little-Wallace]

/label component/ddl

[zimulala]

@GMHDBJD
I checked the log file of debug-log.txt, this test is used "unistore". I tried it. Using "unistore" in the background does reproduce the problem, but using "tikv" does not. We will deal with it.