tidb: support connecting to multi intances directly

Signed-off-by: zyguan <zhongyangguan@gmail.com>

README.md

@@ -130,6 +130,7 @@ Common configurations:
 |mysql.password||MySQL Password|
 |mysql.db|"test"|MySQL Database|
 |tidb.cluster_index|true|Whether to use cluster index, for TiDB only|
+|tidb.instances|""|Comma-seperated address list of tidb instances (eg: `tidb-0:4000,tidb-1:4000`)|
 
 
 ### TiKV

db/mysql/db.go

@@ -16,16 +16,18 @@ package mysql
 import (
 	"bytes"
 	"context"
+	"crypto/sha1"
 	"database/sql"
+	"database/sql/driver"
+	"encoding/hex"
 	"fmt"
 	"strings"
+	"sync/atomic"
 
+	"github.com/go-sql-driver/mysql"
+	"github.com/magiconair/properties"
 	"github.com/pingcap/go-ycsb/pkg/prop"
 	"github.com/pingcap/go-ycsb/pkg/util"
-
-	// mysql package
-	_ "github.com/go-sql-driver/mysql"
-	"github.com/magiconair/properties"
 	"github.com/pingcap/go-ycsb/pkg/ycsb"
 )
 
@@ -40,8 +42,38 @@ const (
 	// TODO: support batch and auto commit
 
 	tidbClusterIndex = "tidb.cluster_index"
+	tidbInstances    = "tidb.instances"
 )
 
+type muxDriver struct {
+	cursor    uint64
+	instances []string
+	internal  driver.Driver
+}
+
+func (drv *muxDriver) Open(name string) (driver.Conn, error) {
+	k := atomic.AddUint64(&drv.cursor, 1)
+	return drv.internal.Open(drv.instances[int(k)%len(drv.instances)])
+}
+
+func openTiDBInstances(addrs []string, user string, pass string, db string) (*sql.DB, error) {
+	instances := make([]string, len(addrs))
+	hash := sha1.New()
+	for i, addr := range addrs {
+		hash.Write([]byte("+" + addr))
+		instances[i] = fmt.Sprintf("%s:%s@tcp(%s)/%s", user, pass, addr, db)
+	}
+	digest := hash.Sum(nil)
+	driver := "tidb:" + hex.EncodeToString(digest[:])
+	for _, n := range sql.Drivers() {
+		if n == driver {
+			return sql.Open(driver, "")
+		}
+	}
+	sql.Register(driver, &muxDriver{instances: instances, internal: &mysql.MySQLDriver{}})
+	return sql.Open(driver, "")
+}
+
 type mysqlCreator struct {
 	name string
 }
@@ -75,10 +107,25 @@ func (c mysqlCreator) Create(p *properties.Properties) (ycsb.DB, error) {
 	user := p.GetString(mysqlUser, "root")
 	password := p.GetString(mysqlPassword, "")
 	dbName := p.GetString(mysqlDBName, "test")
-
-	dsn := fmt.Sprintf("%s:%s@tcp(%s:%d)/%s", user, password, host, port, dbName)
-	var err error
-	db, err := sql.Open("mysql", dsn)
+	tidbList := p.GetString(tidbInstances, "")
+
+	var (
+		db    *sql.DB
+		err   error
+		tidbs []string
+	)
+	for _, tidb := range strings.Split(tidbList, ",") {
+		tidb = strings.TrimSpace(tidb)
+		if len(tidb) > 0 {
+			tidbs = append(tidbs, tidb)
+		}
+	}
+	if len(tidbs) > 0 {
+		db, err = openTiDBInstances(tidbs, user, password, dbName)
+	} else {
+		dsn := fmt.Sprintf("%s:%s@tcp(%s:%d)/%s", user, password, host, port, dbName)
+		db, err = sql.Open("mysql", dsn)
+	}
 	if err != nil {
 		return nil, err
 	}