MySQL Enterprise Monitor 4.0.13 Manual
The agent backlog is a caching mechanism which stores monitoring data in the event the agent cannot communicate with the MySQL Enterprise Service Manager. The backlog can store 10MB of monitored data in active RAM.
Monitoring one MySQL instance: the agent backlog can store up to 40 minutes of monitored data before the backlog cache is filled and data dropped.
Monitoring 10 MySQL instances: the agent backlog can store up to 4 minutes of monitored data before the backlog cache is filled and data dropped.