Monitoring Performance

Let's monitor the time taken by any query in the system. In a real-world application, you would use a telemetry system, but like the email example, we will use the console to log the time taken.

Let's write a new module with an interceptor. Since we want our interceptor to surround each query to get the before and after timestamps, we will use an @around interception.

@deno("time.js")
module Timing {
  @around("query *")
  interceptor time(operation: Operation)
}

For a change, we will implement the logic in JavaScript (TypeScript would have worked just as well). Since we want to measure each query's elapsed time, we will use the performance API.

export async function time(operation) {
  const start = performance.now();
  const result = await operation.proceed();
  const end = performance.now();
  console.log(`'${operation.name()}' took ${end - start} ms`);
  return result;
}

Now rerun any query operation such as concerts. You will see the time taken by the query in the console.

'concerts' took 27.300909 ms

For fun, try the sendNotification mutation. You will see the time taken by the queries made by it.

'concert' took 0.9891450000031909 ms
'subscribers' took 0.8302920000023732 ms

It doesn't matter how the queries are invoked--directly by the user or as a part of some user-implemented logic--the interceptor will measure the time taken.