Remove untick in exchange for increments larger than one

Remove untick from vector clock at the risk of having increments larger than one for the local vector clock in edge cases where persistence of snapshot may fail in the midst of a cycle.

This is an acceptable risk considering the difficulty in implementing transactional IPLD node storage and the application of it in this particular case.

Author: masih

federation/federation.go

@@ -144,11 +144,10 @@ func (f *Federation) snapshot(ctx context.Context, t time.Time) error {
 	node := bindnode.Wrap(newSnapshot, Prototypes.Snapshot.Type()).Representation()
 	headSnapshotLink, err := f.linkSystem.Store(ipld.LinkContext{Ctx: ctx}, Prototypes.link, node)
 	if err != nil {
-		f.vc.untick(f.host.ID())
 		return err
 	}
 	if err := f.setHeadLink(ctx, headSnapshotLink); err != nil {
-		f.vc.untick(f.host.ID())
+		return err
 	}
 	return nil
 }

federation/vector_clock.go

@@ -21,15 +21,6 @@ func (vc vectorClock) tick(id peer.ID) uint64 {
 
 }
 
-// untick decrements the vector clock for the given peer ID.
-// This function is primarily used for error recovery, where incrementing the clock may need to happen first before
-// some state is stored and the state storage itself may fail.
-// As an example, see Federation.snapshot.
-func (vc vectorClock) untick(id peer.ID) uint64 {
-	vc[id] = vc[id] - 1
-	return vc[id]
-}
-
 func (vc vectorClock) reconcile(id peer.ID, c uint64) bool {
 	if vc[id] < c {
 		vc[id] = c

federation/vector_clock_test.go

@@ -24,11 +24,6 @@ func TestVectorClock(t *testing.T) {
 	require.False(t, found)
 	require.Equal(t, uint64(0), clock)
 
-	subject.untick("one")
-	clock, found = subject.clock("one")
-	require.True(t, found)
-	require.Equal(t, uint64(0), clock)
-
 	subject.reconcile("another", 1413)
 	clock, found = subject.clock("another")
 	require.True(t, found)