handle reserved connection in autocommit enabled

Signed-off-by: Harshit Gangal <harshit@planetscale.com>

go/test/endtoend/vtgate/setstatement/sysvar_test.go

@@ -210,11 +210,11 @@ func TestSetSystemVariableAndThenSuccessfulAutocommitDML(t *testing.T) {
 	assertMatches(t, conn, `select @@sql_safe_updates`, `[[INT64(1)]]`)
 
 	checkedExec(t, conn, `update test set val2 = 2 where val1 is null`)
-	assertMatches(t, conn, `select id, val1, val2 from test`, `[[INT64(80) NULL INT64(2)]]`)
+	assertMatches(t, conn, `select id, val1, val2 from test`, `[[INT64(80) NULL INT32(2)]]`)
 	assertMatches(t, conn, `select @@sql_safe_updates`, `[[INT64(1)]]`)
 
 	checkedExec(t, conn, `update test set val1 = 'text' where val1 is null`)
-	assertMatches(t, conn, `select id, val1, val2 from test`, `[[INT64(80) VARCHAR("text") INT64(2)]]`)
+	assertMatches(t, conn, `select id, val1, val2 from test`, `[[INT64(80) VARCHAR("text") INT32(2)]]`)
 	assertMatches(t, conn, `select @@sql_safe_updates`, `[[INT64(1)]]`)
 
 	checkedExec(t, conn, `delete from test where val1 = 'text'`)

go/vt/vtgate/safe_session.go

@@ -214,7 +214,10 @@ func (session *SafeSession) AppendOrUpdate(shardSession *vtgatepb.Session_ShardS
 	session.mu.Lock()
 	defer session.mu.Unlock()
 
-	if session.autocommitState == autocommitted {
+	// additional check of transaction id is required
+	// as now in autocommit mode there can be session due to reserved connection
+	// that needs to be stored as shard session.
+	if session.autocommitState == autocommitted && shardSession.TransactionId != 0 {
 		// Should be unreachable
 		return vterrors.New(vtrpcpb.Code_INTERNAL, "BUG: SafeSession.AppendOrUpdate: unexpected autocommit state")
 	}