Ah, so they're not using the waits. It wouldn't be that surprising if in practice they're just too slow to be practical.
Do you have anything I can read on the rest of what you're saying? It contradicts the HLC paper.
Do you have anything I can read on the rest of what you're saying? It contradicts the HLC paper.
This is hinted at in the HLC paper but it’s not very clear: Section 2 limits the definition of “happens before” to only apply to events which occur on the same node or after a message is received from another node.
One immediate difference between TrueTime and HLC springs to mind though: TT knows the clock ambiguity when the timestamp was generated, HLC does not. So in practice I think TT may see much shorter wait intervals, than HLC which would have to conservative wait out the maximum clock drift estimate allowed.
A skim through the cdb source is consistent with this. It looks like when they hit a read/write conflict where the write has a non-zero logical component in it's HLC stamp, then they wait out any remaining portion of the ambiguity window. Since the max offset is around 400ms, that seems like it could hurt pretty bad under contended writes.
I think HLC would get more interesting if the stamps were extended with the ambiguity interval at stamp time.