Java GraphQL should allow timing instrumentation of the query execution

[bbakerman]

There should be hooks in the implementation such that it would be possible instrument how long queries take.

For example one Ruby implementation

https://rmosolgo.github.io/graphql-ruby/schema/instrumentation#field-instrumentation

uses field wrapping to instrument. This is ok but it requires "opt in" from the schema provider code.

Another way is to have an callback interface that has the beforeFieldResolution() , afterFieldResolution() etc and then have caller insert an implementation of that into the runtime configuration.

The call back would then allow for consumers to use their preferred recording mechanism (JMX, StatsD, DropWizard Metrics etc...)

Another thought is to build a "call graph" of the steps that taken during query resolution and present that back with timings. This might prove too big in practice.

[bbakerman]

Looking more into this specifically its the DataFetchers (aka field resolving) that represents all the time in GraphQL and where (in an operational sense) you will want to know what is happening.

I think the graphql.execution.ExecutionContext is the place to put a ExecutionInstrumentationListener interface in and say its the responsibility of ExecutionService to call that before and after doing some code operation.

I will see if I can get a decent PR up in place for further code discussion...