Instrumentation reporting low numbers when using DataLoader

[patrik-j-nilsson]

I suspect instrumentation only reports time to fetch from cache, not the actual data fetch.

[joemcbride]

It would report how long the particular resolver took. If you're using a cache, it would only reflect the actual data fetch when not pulling the data from the cache.

[patrik-j-nilsson]

Sorry, I meant the data loader's cache.
To me it looks like only LoadAsync is instrumented (fetch from data loader cache).

[joemcbride]

I'm not aware of any metrics captured specific to using a DataLoader. The main metrics being captured are on a per-field (resolver) basis. If that field uses a DataLoader then the time it takes to fetch could be different if pulling from the DataLoader's cache vs. the first time it fetches.

Here's the docs for metrics: https://graphql-dotnet.github.io/docs/getting-started/metrics

And the implementation of InstrumentFieldsMiddleware:

graphql-dotnet/src/GraphQL/Instrumentation/InstrumentFieldsMiddleware.cs

Lines 8 to 25 in 3c7bd27

	public class InstrumentFieldsMiddleware
	{
	public Task<object> Resolve(ResolveFieldContext context, FieldMiddlewareDelegate next)
	{
	var metadata = new Dictionary<string, object>
	{
	{"typeName", context.ParentType.Name},
	{"fieldName", context.FieldName},
	{"returnTypeName", SchemaPrinter.ResolveName(context.ReturnType)},
	{"path", context.Path},
	};
	using (context.Metrics.Subject("field", context.FieldName, metadata))
	{
	return next(context);
	}
	}
	}

[johnrutherford]

It looks to me like the next delegate needs to be awaited in InstrumentFieldsMiddleware for accurate timing with an async resolver.

[joemcbride]

@johnrutherford Ha, duh - yes that would do it.

[RehanSaeed]

@joemcbride There seems to be an implementation of InstrumentFieldsMiddleware built in here which has not been updated yet with an await. Also, is this something that is enabled by default in the server project, I can't quite figure it out?

[joemcbride]

@RehanSaeed Yes, I'm updating that with async/await. Metrics are not enabled by default in the server project. You would need to create your own class that inherits from DefaultGraphQLExecuter<T> so you can add the InstrumentFieldsMiddleware to the ExecutionOptions.

[patrik-j-nilsson]

Thanks for this!

[joemcbride]

This is published in 2.3.0 (along with a few other things)