1. 1 exemplar per bucket is fine; "le +Inf" is also a bucket. (OpenMetrics insists "A bucket MUST NOT have more than one exemplar.", but I don't think the Prometheus code enforces this rule) 2. Prometheus will remember as many exemplars as it can, in a ring buffer. 2b You can't always predict when Prometheus will next scrape. There might be multiple scrapers, e.g. an HA pair.
I'm not sure about 3; maybe some other client authors will comment. As far as I know the Go client retains up to 1 exemplar per series forever. On Tuesday, 27 May 2025 at 22:10:14 UTC+1 feedbac...@gmail.com wrote: > Hi, I'm working on adding exemplar support for histograms to a Haskell > prometheus client. I wanted to run my implementation by Prometheus folks to > see if this all sounds correct: > > 1. For a given histogram with 5 buckets, store up to 1 exemplar per > bucket. Don't store exemplars for +Inf samples. > 2. There should be a minimum retention period, such that if you store two > exemplars for the same bucket back-to-back, only the first exemplar is > stored. My understanding is there are two main purposes of this: > > a. Store fewer exemplars in prometheus > b. Letting callers know up-front if an exemplar is likely to make it to > prometheus, so that they can sample the trace. > > 3. There should be a maximum retention period, such that an exemplar is no > longer sent to prometheus if it's e.g. older than a minute. I'm less clear > on why this is desired, but want to give a good explanation in docs. > > WIP PR here: https://github.com/fimad/prometheus-haskell/pull/74 > -- You received this message because you are subscribed to the Google Groups "Prometheus Developers" group. To unsubscribe from this group and stop receiving emails from it, send an email to prometheus-developers+unsubscr...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/prometheus-developers/3e293706-f3ed-413b-8eb0-68f0a4bfa4aan%40googlegroups.com.
