Example #1
0
// Indirectly this tests that the transaction remembers the NodeID of the node
// being read from correctly, at least in this simple case. Not remembering the
// node would lead to thousands of transaction restarts and almost certainly a
// test timeout.
func TestUncertaintyRestarts(t *testing.T) {
	defer leaktest.AfterTest(t)
	s := createTestDB(t)
	defer s.Stop()
	// Set a large offset so that a busy restart-loop
	// really shows. Also makes sure that the values
	// we write in the future below don't actually
	// wind up in the past.
	offset := 4000 * time.Millisecond
	s.Clock.SetMaxOffset(offset)
	key := roachpb.Key("key")
	value := roachpb.Value{
		Bytes: nil, // Set for each Put
	}
	// With the correct restart behaviour, we see only one restart
	// and the value read is the very first one (as nothing else
	// has been written)
	wantedBytes := []byte("value-0")

	i := -1
	tErr := s.DB.Txn(func(txn *client.Txn) error {
		i++
		s.Manual.Increment(1)
		futureTS := s.Clock.Now()
		futureTS.WallTime++
		value.Bytes = []byte(fmt.Sprintf("value-%d", i))
		if err := engine.MVCCPut(s.Eng, nil, key, futureTS, value, nil); err != nil {
			t.Fatal(err)
		}
		gr, err := txn.Get(key)
		if err != nil {
			return err
		}
		if !gr.Exists() || !bytes.Equal(gr.ValueBytes(), wantedBytes) {
			t.Fatalf("%d: read wrong value: %v, wanted %q", i, gr.Value, wantedBytes)
		}
		return nil
	})
	if i != 1 {
		t.Errorf("txn restarted %d times, expected only one restart", i)
	}
	if tErr != nil {
		t.Fatal(tErr)
	}
}