tidb: fix benchmark go test -test.bench=. -test.run=^XXX (#5791)

bench_test.go

@@ -62,6 +62,10 @@ func prepareSortBenchData(se Session, colType string, valueFormat string, valueC
 	mustExecute(se, "begin")
 	r := rand.New(rand.NewSource(time.Now().UnixNano()))
 	for i := 0; i < valueCount; i++ {
+		if i%1000 == 0 {
+			mustExecute(se, "commit")
+			mustExecute(se, "begin")
+		}
 		mustExecute(se, "insert t (col) values ("+fmt.Sprintf(valueFormat, r.Intn(valueCount))+")")
 	}
 	mustExecute(se, "commit")
@@ -93,7 +97,9 @@ func readResult(goCtx goctx.Context, rs ast.RecordSet, count int) {
 
 func BenchmarkBasic(b *testing.B) {
 	goCtx := goctx.Background()
+	b.StopTimer()
 	se := prepareBenchSession()
+	b.StartTimer()
 	for i := 0; i < b.N; i++ {
 		rs, err := se.Execute(goCtx, "select 1")
 		if err != nil {