Hi Brian,
Thanks for your prompt response.
The dimension I was trying to do the "max" was both - the maximum across
timeseries, and the maximum over time.
So here is what I need: *avg_over_time(max(<metric name>)[5m:1m]) .*
在 2020年5月20日星期三 UTC+8下午7:31:54，Brian Candler写道：
>
> In which dimension are you trying to do the "max" - the maximum across
> timeseries, or the maximum over time?
>
> http_requests_total could be several timeseries each with their own
> labels. Think of it in two dimensions:
>
> http_requests_total{instance="A"} a1 a2 a3 a4 a5
> http_requests_total{instance="B"} b1 b2 b3 b4 b5
> http_requests_total{instance="C"} c1 c2 c3 c4 c5
> ---------------> time
>
> If you want the maximum over time, see
> https://prometheus.io/docs/prometheus/latest/querying/functions/#aggregation_over_time
>
> max_over_time(http_requests_total[5m])
>
> This will return the same set of timeseries as you had before, but for
> each one giving the maximum over the 5 minute window.
>
> http_requests_total{instance="A"} max(a1,a2,a3,a4,a5)
> http_requests_total{instance="B"} max(b1,b2,b3,b4,b5)
> http_requests_total{instance="C"} max(c1,c2,c3,c4,c5)
>
> Aside: this is probably *not* what you want to do with a counter - you
> might want to use rate() on it first. But it makes sense with a gauge.
>
> In the other dimension:
>
> max(http_requests_total)
>
> gives you a single value which is the maximum across all the available
> timeseries: see
> https://prometheus.io/docs/prometheus/latest/querying/operators/#aggregation-operators
>
> As an instant query, you'll get just the most recent time:
>
> http_requests_total max(a5,b5,c5)
>
> but if you graph this, the instant time will be swept over the graph
> window, so you'll see the max across timeseries at each point in time.
> Again, this probably doesn't make sense with counters as they have
> arbitrary offsets, but maximum across gauges makes sense (e.g. show me the
> maximum temperature).
>
> If you want to do aggregation over time on this expression, you can turn
> it back into a range vector using a subquery
> <https://prometheus.io/docs/prometheus/latest/querying/basics/#subquery>:
> e.g.
>
> (max(http_requests_total))[5m:1m]
>
> That calculates the max(http_requests_total) at the current time and at 1
> minute intervals over the previous 5 minutes. You then have a range vector
> that you can aggregate over time.
>
> This is more useful with expressions like:
>
> max_over_time (rate(http_requests_total[5m])[60m:1m])
>
> i.e. calculate the 5-minute average rate at 1 minute intervals, and give
> me the maximum rate seen over the last 60 minutes.
>
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