use json to marshal

Author: lcwangchao

pkg/executor/test/executor/executor_test.go

@@ -564,7 +564,7 @@ func TestTiDBLastTxnInfo(t *testing.T) {
 	tk.MustExec("commit")
 	rows3 := tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts')").Rows()
 	require.Equal(t, strconv.FormatUint(startTS2, 10), rows3[0][0])
-	require.Equal(t, "<nil>", rows3[0][1])
+	require.Equal(t, "0", rows3[0][1])
 
 	// txn explicitly started with begin
 	tk.MustExec("begin")
@@ -590,7 +590,7 @@ func TestTiDBLastTxnInfo(t *testing.T) {
 	tk.MustExec("rollback")
 	rows6 := tk.MustQuery("select json_extract(@@tidb_last_txn_info, '$.start_ts'), json_extract(@@tidb_last_txn_info, '$.commit_ts')").Rows()
 	require.Equal(t, strconv.FormatUint(startTS4, 10), rows6[0][0])
-	require.Equal(t, "<nil>", rows6[0][1])
+	require.Equal(t, "0", rows6[0][1])
 
 	// optimistic txn commit failed
 	tk.MustExec("begin optimistic")

pkg/session/BUILD.bazel

@@ -130,6 +130,7 @@ go_library(
         "@com_github_tikv_client_go_v2//error",
         "@com_github_tikv_client_go_v2//oracle",
         "@com_github_tikv_client_go_v2//tikv",
+        "@com_github_tikv_client_go_v2//txnkv/transaction",
         "@com_github_tikv_client_go_v2//util",
         "@io_etcd_go_etcd_client_v3//:client",
         "@io_etcd_go_etcd_client_v3//concurrency",

pkg/session/session.go

@@ -128,6 +128,7 @@ import (
 	"github.com/pingcap/tidb/pkg/util/tracing"
 	tikverr "github.com/tikv/client-go/v2/error"
 	"github.com/tikv/client-go/v2/oracle"
+	"github.com/tikv/client-go/v2/txnkv/transaction"
 	tikvutil "github.com/tikv/client-go/v2/util"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
@@ -984,10 +985,12 @@ func (s *session) setLastTxnInfoBeforeTxnEnd() {
 		return
 	}
 
-	s.GetSessionVars().LastTxnInfo = fmt.Sprintf(
-		`{"txn_scope": "%s", "start_ts": %d, "for_update_ts": %d}`,
-		txnCtx.TxnScope, txnCtx.StartTS, txnCtx.GetForUpdateTS(),
-	)
+	lastTxnInfo, err := json.Marshal(transaction.TxnInfo{
+		TxnScope: txnCtx.TxnScope,
+		StartTS:  txnCtx.StartTS,
+	})
+	terror.Log(err)
+	s.GetSessionVars().LastTxnInfo = string(lastTxnInfo)
 }
 
 func (s *session) GetClient() kv.Client {