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

Question

I have a Spring Boot application and I am using Spring Boot Actuator and Micrometer in order to track metrics about my application. I am specifically concerned about the 'http.server.requests' metric and the MAX statistic:

{
    "name": "http.server.requests",
    "measurements": [
        {
            "statistic": "COUNT",
            "value": 2
        },
        {
            "statistic": "TOTAL_TIME",
            "value": 0.079653001
        },
        {
            "statistic": "MAX",
            "value": 0.032696019
        }
    ],
    "availableTags": [
        {
            "tag": "exception",
            "values": [
                "None"
            ]
        },
        {
            "tag": "method",
            "values": [
                "GET"
            ]
        },
        {
            "tag": "status",
            "values": [
                "200", 
                "400"

            ]
        }
    ]
}

I suppose the MAX statistic is the maximum time of execution of a request (since I have made two requests, it's the the time of the longer processing of one of them).

Whenever I filter the metric by any tag, like localhost:9090/actuator/metrics?tag=status:200

{
        "name": "http.server.requests",
        "measurements": [
            {
                "statistic": "COUNT",
                "value": 1
            },
            {
                "statistic": "TOTAL_TIME",
                "value": 0.029653001
            },
            {
                "statistic": "MAX",
                "value": 0.0
            }
        ],
        "availableTags": [
            {
                "tag": "exception",
                "values": [
                    "None"
                ]
            },
            {
                "tag": "method",
                "values": [
                    "GET"
                ]
            }
        ]
    }

I am always getting 0.0 as a max time. What is the reason of this?

Answer 1

• What does MAX represent (MAX Discussion)

MAX represents the maximum time taken to execute endpoint.

Analysis for /user/asset/getAllAssets

COUNT  TOTAL_TIME  MAX
5      115         17
6      122         17  (Execution Time = 122 - 115 = 17)
7      131         17  (Execution Time = 131 - 122 = 17)
8      187         56  (Execution Time = 187 - 131 = 56)  
9      204         56  From Now MAX will be 56 (Execution Time = 204 - 187 = 17)  

---

• Will MAX be 0 if we have less number of request (or 1 request) to the particular endpoint?

No number of request for particular endPoint does not affect the MAX (see an image from Spring Boot Admin)

---

• When MAX will be 0

There is Timer which set the value 0. When the endpoint is not being called or executed for sometime Timer sets MAX to 0. Here approximate timer value is 2 to 2.30 minutes (120 to 150 seconds)

DistributionStatisticConfig has .expiry(Duration.ofMinutes(2)) which sets the some measutement to 0 if there is no request has been made for last 2 minutes (120 seconds)

Methods such as public TimeWindowMax(Clock clock,...), private void rotate() Clock interface has been written for the same. You may see the implementation here

---

• How I have determined the timer value?

For that, I have taken 6 samples (executed the same endpoint for 6 times). For that, I have determined the time difference between the time of calling the endpoint - time for when MAX set back to zero

---

MAX property belongs to enum Statistic which is used by Measurement (In Measurement we get COUNT, TOTAL_TIME, MAX)

public static final Statistic MAX

The maximum amount recorded. When this represents a time, it is reported in the monitoring system's base unit of time.

---

Notes: This is the cases from metric for a particular endpoint (here /actuator/metrics/http.server.requests?tag=uri:/user/asset/getAllAssets).

For generalize metric of actuator/metrics/http.server.requests

MAX for some endPoint will be set backed to 0 due to a timer. In my view for MAX for /http.server.requests will be same as a particular endpoint.

---

UPDATE

The document has been updated for the MAX.

NOTE: Max for basic DistributionSummary implementations such as CumulativeDistributionSummary, StepDistributionSummary is a time window max (TimeWindowMax). It means that its value is the maximum value during a time window. If the time window ends, it'll be reset to 0 and a new time window starts again. Time window size will be the step size of the meter registry unless expiry in DistributionStatisticConfig is set to other value explicitly.