GetCurrentDbConnErr returns the last error message (or the empty string if not in an error state) and a timestamp in milliseconds of the last change from OK to error or from error to OK.

StartHeartbeat periodically writes heartbeats to Redis for being monitored by Icinga 2.

UpdateCurrentDbConnErr updates the current error information stored in currentDbConnErr.

WriteStats periodically forwards Stats to Redis for being monitored by Icinga 2.

OngoingSyncStartMilli is to be updated by the main() function.