Prometheus: Surprising (incorrect?) behaviour of "increase" function

[cubranic]

The description for the increase function says that it "calculates the increase in the time series in the range vector." So if I have a counter that's only changed in integer increments, I take it to mean that the result of increase should also be an integer. But that's not what I'm seeing.

I have the following, clearly integer, count samples:

$ curl -gs 'localhost:9090/api/v1/query?query=(http_requests_total{job="api"}[10m])'
{
    "status":"success",
    "data":{
        "resultType":"matrix",
        "result":[
            {
                "metric":{
                    "__name__":"http_requests_total",
                    "instance":"localhost:8080",
                    "job":"api",
                    "method":"foo",
                    "type":"bar"
                },
                "values": [
                    [1494004923.82,"1"],
                    [1494004938.82,"1"],
                    [1494004953.82,"1"],
                    [1494004968.82,"1"],
                    [1494004983.82,"2"],
                    [1494004998.82,"2"],
                    [1494005013.82,"2"],
                    [1494005028.82,"3"],
                    [1494005043.82,"3"],
                    [1494005058.82,"3"],
                    [1494005073.82,"3"],
                    [1494005088.82,"4"],
                    [1494005103.82,"4"],
                    [1494005118.82,"5"],
                    [1494005133.82,"5"],
                    [1494005148.82,"5"],
                    [1494005163.82,"5"],
                    [1494005178.82,"5"],
                    [1494005193.82,"6"],
                    [1494005208.82,"7"],
                    [1494005223.82,"7"],
                    [1494005238.82,"7"],
                    [1494005253.82,"7"],
                    [1494005268.82,"7"],
                    [1494005283.82,"7"],
                    [1494005298.82,"8"],
                    [1494005313.82,"8"],
                    [1494005328.82,"9"],
                    [1494005343.82,"9"],
                    [1494005358.82,"9"],
                    [1494005373.82,"10"],
                    [1494005388.82,"10"],
                    [1494005403.82,"10"],
                    [1494005418.82,"10"],
                    [1494005433.82,"10"],
                    [1494005448.82,"10"],
                    [1494005463.82,"10"],
                    [1494005478.82,"10"],
                    [1494005493.82,"11"],
                    [1494005508.82,"11"]
                ]
            }
        ]
    }
}

But I get non-integer result of "sum(increase(...))":

$ curl -gs 'localhost:9090/api/v1/query?query=sum(increase(http_requests_total{job="api"}[10m]))'
{
    "status":"success",
    "data":{
        "resultType":"vector",
        "result":[
            {
                "metric":{},
                "value":[1494005782.193,"9.23076923076923"]
            }
        ]
    }
}

(Just "increase" is the same value.)

Environment

• System information:

  Linux 3.10.0-514.10.2.el7.x86_64 x86_64
  

• Prometheus version:

  prometheus, version 1.5.2 (branch: master, revision: bd1182d29f462c39544f94cc822830e1c64cf55b)
    build user:       root@a8af9200f95d
    build date:       20170210-14:41:22
    go version:       go1.7.5
  

[juliusv]

@cubranic That's intended behavior, see this timestamped part of @brian-brazil's CloudNativeCon talk: https://www.youtube.com/watch?v=67Ulrq6DxwA&t=15m02s

[juliusv]

@cubranic That said, this is a frequent question, so we should probably mention that in the increase() and rate() documentation.

[cubranic]

Thanks. For the record, the slides are at https://www.slideshare.net/brianbrazil/counting-with-prometheus-cloudnativeconkubecon-europe-2017. Relevant info starts at slide 27.

[lock[bot]]

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