What is Rules "Evaluation Time" and "Last Evaluation"? Do I need to invest time into query tuning?

[Evelyn Pereira Souza]

Hi

What is Rules "Evaluation Time" and "Last Evaluation"?

Dashboard: https://example.org/prom/new/rules

Most is some value like "0.xxxms" which seems fast

But this
node_systemd_unit_state{instance=~".+yyy.+",name=~"bbb.+",state="failed"}
== 1 is 3.635ms

and

probe_ssl_earliest_cert_expiry{module=~".+-mmm-.+example.org.+|.+-ppp-.+example.net.+"}
- time() < 86400 * 30 is 16.605ms

Do I need to invest time into query tuning?

best regards

Evelyn

[Matthias Rampke]

No, these are still very very fast. You only need to worry when it gets into the range of several seconds.

Prometheus evaluates rules on a timer (typically every 10s to 1m, depending on your configuration), the "last evaluation time" is how long ago that last happened. If a rule group is still evaluating when the time comes to start again, an evaluation is skipped, this is when you need to worry.

Some rules evaluate in under a millisecond if they have no or only in-memory data to look at (few time series, short time intervals). But 16ms is still plenty fine, especially for recording rules.

/MR

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