roachpb: ignore error timestamp when restarting aborted txn

The local hlc should have been advanced to at least the error's
timestamp by the time PrepareTransactionForRetry is called.

Release note: None

pkg/kv/txn_coord_sender_test.go

@@ -676,7 +676,7 @@ func TestTxnCoordSenderTxnUpdatedOnError(t *testing.T) {
 	ctx := context.Background()
 	origTS := makeTS(123, 0)
 	plus10 := origTS.Add(10, 10)
-	plus20 := plus10.Add(10, 0)
+	plus20 := origTS.Add(20, 0)
 	testCases := []struct {
 		// The test's name.
 		name             string
@@ -778,6 +778,10 @@ func TestTxnCoordSenderTxnUpdatedOnError(t *testing.T) {
 				if pErr == nil {
 					reply = ba.CreateReply()
 					reply.Txn = ba.Txn
+				} else if txn := pErr.GetTxn(); txn != nil {
+					// Update the manual clock to simulate an
+					// error updating a local hlc clock.
+					manual.Set(txn.Timestamp.WallTime)
 				}
 				return reply, pErr
 			}

pkg/roachpb/data.go

@@ -1153,20 +1153,17 @@ func PrepareTransactionForRetry(
 		// TODO(andrei): Should we preserve the ObservedTimestamps across the
 		// restart?
 		errTxnPri := txn.Priority
-		// The OrigTimestamp of the new transaction is going to be the greater of
-		// two the current clock and the timestamp received in the error.
-		// TODO(andrei): Can we just use the clock since it has already been
-		// advanced to at least the error's timestamp?
+		// Start the new transaction at the current time from the local clock.
+		// The local hlc should have been advanced to at least the error's
+		// timestamp already.
 		now := clock.Now()
-		newTxnTimestamp := now
-		newTxnTimestamp.Forward(txn.Timestamp)
 		txn = MakeTransaction(
 			txn.Name,
 			nil, // baseKey
 			// We have errTxnPri, but this wants a UserPriority. So we're going to
 			// overwrite the priority below.
 			NormalUserPriority,
-			newTxnTimestamp,
+			now,
 			clock.MaxOffset().Nanoseconds(),
 		)
 		// Use the priority communicated back by the server.