> Hello - It seems that the replication heartbeat is not configurable. In
> 1.8 it was (did not check 2.0). Are there any details on how heartbeat and
> fail-over timings work? What is the timing on fail-overs now (it seems
> fast - but need to understand). We are looking to get sub second fail-over
> working in an environment where all machines are on a single switch.
You are correct that the replication heartbeat is not configurable. The
heartbeat request can either receive a response, an error, or a timeout.
Failover should happen within ~20 seconds.
The current documentation
Failing too fast (sub-second, in particular) generally isn't a
positive/desirable outcome as you can cause flapping in the event of
transient network issues.
The replica set failover is generally still faster than the default TCP
timeout setting (which, depending on your O/S, can be up to a few minutes).