Ah, that makes sense! Thanks for the explanation, I'm new to Prometheus so it wasn't obvious to me.
If it helps the next newbie, I made a pull request to add a bit more explicit documentation about this, to clarify the parts that confused me: https://github.com/prometheus/prometheus/pull/7141 On Friday, April 17, 2020 at 1:43:25 PM UTC+1, Brian Candler wrote: > > On Friday, 17 April 2020 12:46:01 UTC+1, Alex Rosen wrote: >> >> This page >> <https://prometheus.io/docs/prometheus/latest/configuration/alerting_rules/> >> says: >> "The $value variable holds the evaluated value of an alert instance." >> >> It would be great if this also included a more explicit definition, >> because this definition isn't obvious to me. For example, if I have: >> >> >> expr: sum(increase(some_counter[3h])) by (foo) < 1 >> >> >> Which part of this is the $value? It can't be the entire expression, >> because that's just a boolean value. Is it everything to the left of the >> comparison operator? >> > > It *is* the value of the entire expression. > > The prometheus operator "a < b" gives the value of the left-hand side if > it's less than b (scalar, or timeseries with exactly matching label set), > or no result if not. See comparison operators > <https://prometheus.io/docs/prometheus/latest/querying/operators/#comparison-binary-operators> > . > > You can try this for yourself in the PromQL expression evaluator in the > prometheus UI: e.g. > > rate(node_network_receive_bytes_total[2m]) > 10000 > > You'll see line segments where the condition is true, and gaps where it's > false. > > [image: png1.png] > > > There is another form: "a < bool b", which gives 0 for false and 1 for > true. In that case, the timeseries always exists, and $value will be > either 0 or 1 (which for alerts makes it less useful in annotations) > -- You received this message because you are subscribed to the Google Groups "Prometheus Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/prometheus-users/43672c22-bed6-40bf-aeff-1cd82d962e16%40googlegroups.com.
