Is there a way to provide different buckets for Prometheus histogram?

In Prometheus, default histogram is defined as:

private double[] buckets = new double[]{.005, .01, .025, .05, .075, .1, .25, .5, .75, 1, 2.5, 5, 7.5, 10};

It is used in org/http4s/metrics/prometheus/Prometheus.scala:157 to measure response times.

The default bucket has good steps at start, but at is quite useless at end with resolution of 2.5s.

It would be nice, if there would be a way to set own bucket list, but I didn’t find such. Maybe it would be good idea to use custom bucket list, like:

responseDuration = Histogram
  .build()
  .buckets(0.005, 0.01, 0.02, 0.04, 0.08, 0.1, 0.2, 0.4, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, 5.2, 5.4, 5.6, 5.8, 6, 6.2, 6.4, 6.6, 6.8, 7, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.6, 8.8, 9, 9.2, 9.4, 9.6, 9.8, 10)
  //...

It has more than 4x buckets and has a bit better resolution on “fast” end and much better one on “slow” end, resolution is closer to linear - this can be useful in cases, when generated response depends on slow backend system(s). It could be even useful to add 0.5 steps up to 20 seconds.

[mr-git]

Current http4s API doesn’t expose this ability and uses default bucket, which is quite shallow and wide… Options:

• use the buckets as I mentioned in main
• close this as “not an issue” and forget about it
• complicate current API and expose ability to provide custom bucket list

[mr-git]

0.20.x is sufficient. thanks for letting me know!