On 23 Jul 01:04, Marek Skalicky wrote:
> Hi,
> I'm running prometheus with lookback-delta=9m and scraping a metric every 5
> minutes. I've seen issue when evaluating
> 'increase(ifHCInOctets{network_key="xxx"}[10m])/2' in recording rule.
> I've reported that as a bug in
> https://github.com/prometheus/prometheus/issues/9092, but I was told the
> lookback-delta should be 15m so it's an issue of configuration.
>
> But when I do the same query in grafana it shows correctly. So does the
> lookback-delta have special meaning for recording rules?
> My understanding was that the lookback delta is used per individual data
> points, so the fact that the query/rule has range vector 10m has nothing to
> do with the lookback delta. I have also recording rules doing "the same"
> with 1h and 24h range vector and those work fine.
>
> Could anyone please explain why I should use 15m lookback-delta?
In your case you have a very low scrape interval, 300s. That means that
for your prometheus server, if you query data, you would find some
oddities with the default lookback delta.
When I did look at the issue, I did not notice that you were using
increase. Then, loopback delta does not play a role. Instead, you should
use:
irate(ifHCInOctets{network_key="xxx"}[15m])
which seems a better option.
15 min should ensure there is at least 2 datapoints, and irate will do
the calculation between the last 2 datapoints.
>
> Many thanks,
> Marek Skalicky
>
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Julien Pivotto
@roidelapluie
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