Splunk documentation about metrics.log is nice but not entirely up to date and complete according to me.
In section "Tcpout connections messages", we are missing the aggregation parameter for the values. Is the data reported (like _tcp_KBps) by "name", by "destIp" , by something else ... ? I've tried to figure this out by graphing _tcp_KBps over time and use different aggregation parameters but I have never been able to get a continuous line with a growing value (which should be the case).
From time to time another field named "one_time_client=1" appears. What does it mean ?
When UseACK is true, you get 2 additional metrics : max_ackq_size and current_ackq_size. They are not documented as far as I know, what do they mean ?