Hybrid Logical Clocks (HLC) provide a one-way causality detection using a combination of logical time and physical NTP timestamp. This library adds an additional mechanism for resolving conflicts between timestamps by adding a unique node id to each HLC timestamp.

These timestamps can be used in place of standard NTP timestamps in order to provide consistent snapshots and causality tracking. HLCs have a fixed space requirement and are bounded close to physical timestamps.

First, add HLClock to your mix.exs dependencies.

def deps do
  [{:hlclock, "~> 1.0"}]
end

Starting in version 1.0.0, the HLClock.Server is not started as an application automatically. HLClock.start_link/1 is as a short cut to manually start a process:

{:ok, clock} = HLClock.start_link()
{:ok, ts} = HLClock.send_timestamp(clock)

In practice, it is best to have a single HLClock running on any given node. Toward that end, HLClock also provides a child_spec that accepts all standard GenServer opts:

children = [
  {HLClock, name: :my_hlc_server},
]