No data in $SYS/broker/messages/inflight

[fschlager]

I'm running Mosquitto v2.0.15 in Kubernetes on Linux.
The documentation states that the following statistic is available:

$SYS/broker/messages/inflight

    The number of messages with QoS>0 that are awaiting acknowledgments.

Yet when I try to read data from it it always comes back empty. Also a quick skim through the code gave no indication that this topic is ever being written to.

I'm trying to monitor this value to detect possible bottlenecks in our setup.

Am I missing something?