Reading Traces

Let's take a closer look at a full trace in Jaeger. This is my "create shortlink" trace:

You should have seen something similar in the last lesson. Notice a few things:

1. The auth.validate_password span takes a long time. That makes sense; it's checking a password hash.
2. The handler.shorten_link span is the actual business logic of the request
3. The http.verify_destination child span is taking almost all of the time of the handler.shorten_link span.

This check was added with good intentions – who wants to redirect users to a broken link? – but it runs on every shortlink creation request and, aside from auth, is the hottest path in the application.

It tells us something simple: checking the destination URL is by far the most expensive part of the "create shortlink" operation: much slower than actually saving the link to disk.