Why is replication stopped? Got the following nagios alert this morning for our MySQL replica:


  14:49 PROBLEM: mysql2/MySQL replication check is CRITICAL, 10.1.0.133 is 72870 seconds behind, Aug 09, 21:49 UTC


When I look at SHOW SLAVE STATUS on the replica, the places I normally look at are fine:

Slave_IO_State: Waiting for master to send event
Seconds_Behind_Master: 73698
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Last_IO_Errno: 0
Last_SQL_Errno: 0


Where else should I be looking to diagnose and fix replication?
Has anything been written to the Master in the last 72K seconds (about a day)?

Sometimes this helps:

STOP SLAVE;
START SLAVE;


I have seen the need for this on and off over the last decade; never figured out why it might be needed.

Another mystery is that the Seconds_behind_master sometimes mysteriously decides to flap between zero and some large value.  Eventually that problem clears itself up.