Updates the doc of the heartbeat field of RaftMetrics and RaftDataMetrics as we store the timestamp itself rather than the duration since the last acknowledged heartbeat/replication timestamp since #1202.
Checklist
[ ] Updated guide with pertinent info (may not always apply).
[x] Squash down commits to one or two logical commits which clearly describe the work you've done.
What does this PR do
Updates the doc of the
heartbeatfield ofRaftMetricsandRaftDataMetricsas we store the timestamp itself rather than the duration since the last acknowledged heartbeat/replication timestamp since #1202.Checklist
This change is