Side note: In Java this would be particularly useful because the popular
Spring Boot framework exposes a Summary http_server_requests_seconds by
default that look like this (no quantiles, just _count and _sum):
# HELP http_server_requests_seconds
# TYPE http_server_requests_seconds summary
http_server_requests_seconds_count{exception="None",method="GET",outcome="SUCCESS",status="200",uri="/",}
1.0
http_server_requests_seconds_sum{exception="None",method="GET",outcome="SUCCESS",status="200",uri="/",}
1.014687278
I think this is pretty useful, you can get request rates and error rates
out of it. If Prometheus / OpenMetrics had support for Exemplars on the
_count, users could find example traces per HTTP status and URI.
Fabian
On Tue, Oct 18, 2022 at 3:05 PM Bjoern Rabenstein
wrote:
> On 06.10.22 14:45, 'Fabian Stäber' via Prometheus Developers wrote:
> >
> > Great question from the CNCF Slack: What's the reason why we don't allow
> > Exemplars for _count in Summary metrics?
> >
> > What do you think? Any reason why Exemplars don't work in _count in
> > Summaries? Would that be something we could consider supporting?
>
> The _count of a Summary _and_ the _count of a Histogram (both
> conventional as well as the new native ones) is essentially a counter
> within the larger "structured" metric of a Summary/Histogram.
>
> From that perspective, it should have the option of attaching an
> examplar, as a regular Counter has, too.
>
> My speculation why it doesn't in OpenMetrics:
>
> In an OM Histogram, the +Inf bucket fulfills exactly the same function
> as the _count (spec says: "The +Inf bucket counts all requests.") So
> if you would like an examplar on the _count of a Histogram, you can as
> well use an exemplar on the +Inf bucket.
>
> That obviously doesn't help in the case of a Summary, but I guess the
> rationale is that Histograms are generally to be preferred over
> Summaries, and therefore didn't get the thourough treatment when it
> came to exemplars.
>
>
> However, even if you really dislike the precalculated quantiles in
> Summaries, there is still the case of a Summary without quantiles. I
> think adding exemplars to such a Summary is as much needed as adding
> exemplars to any regular Counter.
>
> --
> Björn Rabenstein
> [PGP-ID] 0x851C3DA17D748D03
> [email] bjo...@rabenste.in
>
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