Spring Boot Actuator 'http.server.requests' metric MIN time

Question

The actuator endpoint /actuator/metrics/http.server.requests can exhibit this informations:

{
  "name": "http.server.requests",
  "baseUnit": "seconds",
  "measurements": [
    {
      "statistic": "COUNT",
      "value": 17.0
    },
    {
      "statistic": "TOTAL_TIME",
      "value": 0.751589096
    },
    {
      "statistic": "MAX",
      "value": 0.379677657
    }
  ],
  "availableTags": [
    {
      "tag": "exception",
      "values": [
        "none"
      ]
    },
    {
      "tag": "method",
      "values": [
        "GET"
      ]
    },
    {
      "tag": "error",
      "values": [
        "none"
      ]
    },
    {
      "tag": "uri",
      "values": [
        "/swagger-ui*/**",
        "/v3/api-docs/swagger-config",
        "/v3/api-docs",
        "/simulacao",
        "/swagger-ui*/*swagger-initializer.js"
      ]
    },
    {
      "tag": "outcome",
      "values": [
        "SUCCESS"
      ]
    },
    {
      "tag": "status",
      "values": [
        "200"
      ]
    }
  ]
}

I want to add a measurement statistic called "MIN" that shows the min time requests took, like this:

{
  "name": "http.server.requests",
  "baseUnit": "seconds",
  "measurements": [
    {
      "statistic": "COUNT",
      "value": 17.0
    },
    {
      "statistic": "TOTAL_TIME",
      "value": 0.751589096
    },
    {
      "statistic": "MAX",
      "value": 0.379677657
    },
    {
      "statistic": "MIN",
      "value": 0.001235678
    }
  ],
  "availableTags": [
    {
      "tag": "exception",
      "values": [
        "none"
      ]
    },
    {
      "tag": "method",
      "values": [
        "GET"
      ]
    },
    {
      "tag": "error",
      "values": [
        "none"
      ]
    },
    {
      "tag": "uri",
      "values": [
        "/swagger-ui*/**",
        "/v3/api-docs/swagger-config",
        "/v3/api-docs",
        "/simulacao",
        "/swagger-ui*/*swagger-initializer.js"
      ]
    },
    {
      "tag": "outcome",
      "values": [
        "SUCCESS"
      ]
    },
    {
      "tag": "status",
      "values": [
        "200"
      ]
    }
  ]
}

I'm using Springboot and I was not able to find information about creating statistics on Micrometer documentation. Can someone help me understand how to approach this problem?

Jonatan Ivanov · Accepted Answer · 2025-09-03 22:57:08Z

Min is a bit problematic, let me explain it from the perspective of max. Max is not a "global maximum" which means it is not the max of all the recorded latencies ever but it is a "time-window max" which means it shows you a "recent" maximum value, see the docs:

The maximum statistical value for basic Timer implementations [...] is a time window maximum (TimeWindowMax). It means that its value is the maximum value during a time window. If no new values are recorded for the time window length, the max is reset to 0 as a new time window starts.

source: https://docs.micrometer.io/micrometer/reference/concepts/timers.html

One of the reasons behind this is when the app starts, processing things (e.g.: http requests) is usually slower (lazy init, cache population, no JIT compilation, etc). So a "global maximum" would not be very useful. You can find the other reason using a time-window max in the docs at the same section I quoted above.

So let's say you also want to implement min and you might want to make it time-windowed. In this case, where should min decay to? And what should be the value if no recordings happened in a time-window?

But if your metrics backend supports histograms, you might be able to calculate the 0th percentile which should approximate min. (It is also possible doing this in a MeterRegistry, the Dynatrace V2 implementation in Micrometer does exactly this, see DynatraceExporterV2).

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