ActivitySource vs DiagnosticSource

[aunikitin]

Hello!
First of all, a small context:
I want to build my own metrics for Npgsql driver and I use EF Core + Npgsql.
For example, some histogram for measurement db statements from pod instance point of view. I asked guys from npgsql about this and they said that it's better to implement it by myself using their ActivitySource (NpgsqlActivitySource). (our discussion somewhere at the end) to catch traces and did whatever I want with them. After that I was inspired, and try to do it.
I copied your ListenerHandler infrastructure, realized my simple trace handler (without any logic, only catching an activity), but unfortunately I got nothing.
First of all, every time, when I added my handler via TracerProviderBuilder:

var instrumentation = new NpgsqlMetrics("Npgsql", options);
builder.AddSource("Npgsql");
return builder.AddInstrumentation(() => instrumentation);

I cought Microsoft.EntityFramework as DiagnositcListener in my OnNext method. After some searching I found out, that internally we have chain of listeners, and EF Core creating their own DiagnosticSource when you create DbContext. I tried to add DiagnosticSource("Npgsql") by my own, naively expecting that it'll help. After that I began recieving Npgsql-diagnostic listener in my OnNext method, but stil without triggering my custom listener.

DiagnosticSource != ActivitySource that is used in Npgsql driver and my question is how to coupe with OpenTelemetry, ActivitySource (from Npgsql), DiagnosticSource and registering infrastructure(such as DiagnosticSourceListener, DiagnosticSourceSubscriber, ListenerHandler) from OpenTelemetry?
If I should read some paper before asking, please give me a link

[utpilla]

I asked guys from npgsql about this and they said that it's better to implement it by myself using their ActivitySource (NpgsqlActivitySource).

If they have told you to use their ActivitySource, there are two obvious approaches to achieving what you want:

1. You could either create an ActivityListener and configure it accordingly to listen to the activities created by their ActivitySource. With this approach, you would have to be careful with the order of registration of ActivityListeners (as OpenTelemetry Tracing SDK also creates its own ActivityListener) and ensure that you don't mess up with the sampling of activitites.

2. You could use a custom processor that would emit the required metrics when the activity is started or stopped. You'll have to add this custom processor to the TracerPorvider so that it can call the custom processors' methods on activity start and stop. Something like this:

using var tracerProvider = Sdk.CreateTracerProviderBuilder()
    .AddSource("Npgsql")
    .AddProcessor(new NpgSqlMetricsProcessor())
    .Build();

public class NpgSqlMetricsProcessor : BaseProcessor<Activity>
{
    internal Meter CustomMeter = new Meter("CustomMeter");
    internal Histogram<double> CustomMetric;
    
    public NpgSqlMetricsProcessor()
    {
        this.CustomMetric = this.CustomMeter.CreateHistogram<double>("CustomMetric");
    }

    public override void OnStart(Activity activity)
    {
    }

    public override void OnEnd(Activity activity)
    {
        if (activity.Source.Name == "Npgsql" && activity.DisplayName == "ExpectedActivityName")
        {
            this.CustomMetric.Record(activity.Duration.TotalMilliseconds, new KeyValuePair<string, object?>("Status", activity.Status));
        }
    }
}

[aunikitin]

Thanks for reply. I'll try this on weekends!

[aunikitin]

I tried BaseProcessor implementation. It works perfect, thanks!