micrometer-metrics
Use exemplar for Timer max value.
Please describe the feature request. If I understand correctly, exemplars are only collected for timer with distributionStatistics set to "prometheus". I think it wille be usefull to have exemplar for max value in a timer even if histogram are not enabled.
Rationale I wan't to be able to easily correlate the longest occurences with my traces and logs.
TL;DR: You can simulate this with a histogram and calculating the 100%'ile (using histogram_quantile but yes, you need to enable histogram for this).
Details: Right now we support Exemplars as defined in the OpenMetrics specification. This means Prometheus counters and histogram buckets.
Timer's max value is a Prometheus gauge, that's the reason why Exemplars are missing right now from max: OpenMetrics does not support Exemplars for gauges.
Other than this, I'm with you, I don't have the full context for OpenMetrics specs but I find having Exemplars on max useful.
There is a PR and a separate discussion around a similar functionality (lack of Exemplars on count for Timer/Distribution): https://github.com/micrometer-metrics/micrometer/pull/3460
Let me include this in the discussion there to see if we can put exemplars on gauges.
Blocked on the outcome of https://github.com/micrometer-metrics/micrometer/pull/3460