TimerHandler implementation always records nanoseconds in Histogram

[t089]

I am a bit confused about how to use the Histogram style of metrics successfully with swift-metrics.

When interacting with the Timer interface from swift-metrics you can specify the unit of your time measurements. But when configuring PrometheusMetricsFactory I cannot specify the unit of my histogram buckets. If I use the default values ([0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10]), most measurements will end up in the +Inf bucket, because internally the MetricsHistogramTimer always records nanoseconds. I think the only way to make it work right know would be to change the buckets to be in ns, [0.005e9, 0.01e9, 0.025e9, 0.05e9, 0.1e9, 0.25e9, 0.5e9, 1e9, 2.5e9, 5e9, 10e9] which seems quite unintuitive.

Probably it would make sense to default to seconds for the unit and change the MetricsHistogramTimer implementation to convert the nanoseconds to seconds. Since this is a global setting it will apply to ALL "timer" metrics emitted by any library in the process. So maybe this should be part of the TimerImplementation configuration.

Example

let prometheusClient = PrometheusClient()
MetricsSystem.bootstrap(PrometheusMetricsFactory(client: prometheusClient,
                                                 configuration: .init( timerImplementation: .histogram())))

let timer = Timer(label: "my_timer")

timer.record(.seconds(5))

prometheusClient.collect { (metrics : String) -> () in
    print(metrics)
}

# TYPE startup_time histogram
startup_time_bucket{le="0.005"} 0
startup_time_bucket{le="0.01"} 0
startup_time_bucket{le="0.025"} 0
startup_time_bucket{le="0.05"} 0
startup_time_bucket{le="0.1"} 0
startup_time_bucket{le="0.25"} 0
startup_time_bucket{le="0.5"} 0
startup_time_bucket{le="1.0"} 0
startup_time_bucket{le="2.5"} 0
startup_time_bucket{le="5.0"} 0
startup_time_bucket{le="10.0"} 0
startup_time_bucket{le="+Inf"} 1
startup_time_count 1
startup_time_sum 5000000000

• Swift version: 5.6.1
• Framework version: 1.0.0
• swift-metric: 2.3.1