Batch export vs periodic exporting with OLTP exporter

[tomkerkhove]

Question

Describe your environment.

We are using the OTLP exporter with the default settings:

var configuredMetricProvider = Sdk.CreateMeterProviderBuilder()
                .AddMeter("Sample.*")
                .AddOtlpExporter(options => { options.Endpoint = new Uri(collectorUri); })

What are you trying to achieve?

We are using the OTLP exporter and want to understand what the interval is in which metrics will be flushed.

However, I'm not sure how options.BatchExportProcessorOptions.ScheduledDelayMilliseconds & options.PeriodicExportingMetricReaderOptions.ExportIntervalMilliseconds relate with each other.

I had the impression that one or the other is being used, but based on the default values they should both be used. (based on reading the code):

opentelemetry-dotnet/src/OpenTelemetry.Exporter.OpenTelemetryProtocol/OtlpExporterOptions.cs

Lines 115 to 130 in 1191a2a

	public ExportProcessorType ExportProcessorType { get; set; } = ExportProcessorType.Batch;
	/// <summary>
	/// Gets or sets the BatchExportProcessor options. Ignored unless ExportProcessorType is Batch.
	/// </summary>
	public BatchExportProcessorOptions<Activity> BatchExportProcessorOptions { get; set; } = new BatchExportActivityProcessorOptions();
	/// <summary>
	/// Gets or sets the <see cref="MetricReaderType" /> to use. Defaults to <c>MetricReaderType.Periodic</c>.
	/// </summary>
	public MetricReaderType MetricReaderType { get; set; } = MetricReaderType.Periodic;
	/// <summary>
	/// Gets or sets the <see cref="PeriodicExportingMetricReaderOptions" /> options. Ignored unless <c>MetricReaderType</c> is <c>Periodic</c>.
	/// </summary>
	public PeriodicExportingMetricReaderOptions PeriodicExportingMetricReaderOptions { get; set; } = new PeriodicExportingMetricReaderOptions();

Additional Context

N/A

[alanwest]

This is admittedly a little confusing at the moment.

ExportProcessorType and BatchExportProcessorOptions is only used for trace data at the moment.

MetricReaderType and PeriodicExportingMetricReaderOptions are used for metric data.

So, that's to say that options.BatchExportProcessorOptions.ScheduledDelayMilliseconds and options.PeriodicExportingMetricReaderOptions.ExportIntervalMilliseconds do not relate to each other. First one is used by the OTLP trace exporter and the second one used by the OTLP metrics exporter.

There's some works in progress exploring some different concepts for making the exporter's configuration more intuitive. (#2717 and #2721).

---

Ideally, ExportProcessorType and BatchExportProcessorOptions would not have been included on the OtlpExporterOptions class as they are not used for configuring the exporter at all. They're used for configuring the processor. The pipeline for traces and metrics differ architecturally in that there is no notion of a metric processor, so that's why these options do not relate to metrics.

[tomkerkhove]

Thanks for explaining! Would it make sense if I send a PR to update the XML docs with this info? (trace vs metric)

[alanwest]

You might wait just a bit. We'll settle on an approach in one of the PRs in progress soon. What we do there may influence how to best document things. I agree we need to make this more clear.

[tomkerkhove]

Sounds good to me and thanks for the help.

Will close the issue for now.