It will be useful for identifying mongod instances where flow control has been engaged to have cumulative metrics about the number of times flow control has been engaged on a mongod instance since startup, and the cumulative time for which flow control has been engaged. For the purposes of this ticket, flow control being "engaged" means the isLagged metric is 1, i.e., the current majority committed lag is greater than some established threshold percentage of the configured target maximum lag. These new metrics would be based on the isLagged metric, so maybe these could be named

• isLaggedCount - incremented every time isLagged goes from 0 to 1
• isLaggedTimeMicros - incremented every time isLagged goes to 0 by the elapsed time since it last went to 1.