2.2 Tick Management

In the description of the vector clock algorithm above, the tick is incremented every time a resource is modified. This is actually not a requirement and the algorithm works just as well if the tick is incremented when the modification is detected as part of a synchronization pass rather than at the time the modification actually happened. So the algorithm does not impose that we be able to trap modifications in real time.

Even when ticks are only set at the beginning of a synchronization pass, every entry in a sync feed must receive a different tick value and the tick values must increase for a given endpoint as we walk a sync feed from beginning to end. This rule is not really imposed by the vector clock algorithm but it is imposed by SData Sync because it allows the engine to resume a sync at the point where it was interrupted rather than at the beginning of the sync feed.

SData uses the convention that the clock tick be incremented “after” being recorded in the vector clock rather than before being recorded. So the tick should be interpreted as the “first clock value not yet assigned”, not as the “last clock value assigned”.