MQTT Updates

[starsoccer]

How often should data published via mqtt be updated, or is data only updated when an actual change takes place? Asking as I see some data that gets updated every few seconds, and then other points that seem to get 2 or 3 updates, and then never update again.

A good example of this is cooling set point. It gets updated when started, and then never updates again.

[ccutrer]

Any particular value is only published to MQTT when it changes (and at startup, to set the initial state). All messages are sent retained, so even if a subscriber wasn't around when it was originally sent, they'll still get the most recent value.

[starsoccer]

Okay thanks. Is there anyway to tell if the data has simply not changed vs being stale?

For context on my use case, I am looking at using telegraf to pipe mqtt values into influx to have charts in grafana. While it works OK as is, telegraf only pipes data when a message is published(I believe). So what ends up happening currently is telegraf starts, takes current data and broadcasts it, then it is never broadcasted again and a chart ends up looking a bit ridiculous like this:

There may be a better solution to this within telegraf but Im not super familiar with it generally

[starsoccer]

Well right after posting I was able to resolve this. For anyone else who hits this under the query options you can choose a fill option and select previous for it to just backfill the value