StartTimeUnixNano is always set to "11651379494838206464" using v0.37.0 version of go.opentelemetry.io/otel/metric

[anil181]

I am using Int64ObservableGauge instrument with callback (RegisterCallback) to record a metric with NewPeriodicReader and export it to otel collector. Below is the code on how am doing it:

			observable, _ := meter.Int64ObservableGauge(
				fullName,
				instrument.WithDescription(metricDescription),
			)


			//callback function can be updated periodically w/o necessity to create new instance of instrument
			registration, _ := meter.RegisterCallback(func(_ context.Context, o metric.Observer) error {
				if bObserve {
					o.ObserveInt64(observable, metricValue, statsLabels...)
					bObserve = false
				}
				return nil
			}, observable)

But with all the metric being sent i see the startTimeUnixNano is always set to "11651379494838206464", however the timeUnixNano is set properly.

excerpt from the oltp.json

                     "gauge":{
                        "dataPoints":[
                           {
                              "attributes":[
                                 {
                                    "key":"applicationName",
                                    "value":{
                                       "stringValue":"imperative:application"
                                    }
                                 },
                                 {
                                    "key":"metricName",
                                    "value":{
                                       "stringValue":"clientside.max_conns"
                                    }
                                 },
                                 {
                                    "key":"metricProperty",
                                    "value":{
                                       "stringValue":"/app/imperative:application/stack/imperative:stack"
                                    }
                                 },
                                 {
                                    "key":"metricType",
                                    "value":{
                                       "stringValue":"my_server_stat"
                                    }
                                 },
                                 {
                                    "key":"stackName",
                                    "value":{
                                       "stringValue":"imperative:stack"
                                    }
                                 },
                                 {
                                    "key":"systemId",
                                    "value":{
                                       "stringValue":"edd50c42-c08c-e2bb-bcb6-a912e090ecd0"
                                    }
                                 }
                              ],
                              "startTimeUnixNano":"11651379494838206464",
                              "timeUnixNano":"1685016941030560013",
                              "asInt":"0"
                           }
                        ]
                     }

Earlier we were using meter.AsyncInt64().Gauge from v0.31.0 version of go.opentelemetry.io/otel/metric and the startTimeUnixNano was populated with the same value as that of timeUnixNano.

I could not find a way to set the value of startTimeUnixNano, could you please guide on fixing this?

Thanks & regards,
Anil

[pellared]

The values are set by the SDK. Why do you think the values are wrong? Please see: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/data-model.md#gauge

[pellared]

The value is indeed strange. Recently I got a valid value: #4133 (comment)

Can you please:

1. Try using the latest version.

If the bug persists then:

2. Create a bug with minimal reproducible example

[anil181]

The difference between my and your example is that am using asynchronous instrument Int64ObservableGauge while in #4133 (comment) you are using synchronous Float64UpDownCounter. Have you tried with asynchronous instrument?

[pellared]

I have managed to reproduce it and I agree that this is a bug. I will create an issue as I already have some repro steps. I also found places in code that should be investigated while fixing.

[pellared]

I created #4268 and #4269

could you please guide on fixing this?

I started working on #4268

Regarding #4269 you can take a look and consider contributing 😉

[anil181]

Thank you @pellared for reproducing the issue on your end and proposing the fix. For #4269 "A timestamp (start_time_unix_nano) which best represents the first possible moment a measurement could be recorded. This is commonly set to the timestamp when a metric collection system started." the statement is not lucid and i see you following up on the clarification.