Measure your own code

The per-view numbers tell you the view is slow. They don’t tell you which twenty lines of it. For that you time the block yourself, and django-statsd gives you two ways in.

Through the request

Inside a tracked request, request.statsd is that request’s timer. Use it as a context manager, or start and stop it by hand when the two ends sit far apart.

def some_view(request):
    with request.statsd.timings('build_queryset'):
        ...

def some_other_view(request):
    request.statsd.timings.start('build_queryset')
    ...
    request.statsd.timings.stop('build_queryset')

Through the module

When the code doing the work has no request to hand, the module-level helpers reach the same scope from anywhere. I use the context manager almost everywhere. start and stop only earn their place when the two ends sit in different methods.

import django_statsd

with django_statsd.with_('payment.authorise'):
    ...

django_statsd.incr('payment.attempt')
django_statsd.decr('payment.attempt')

@django_statsd.decorator('payment')
def authorise():
    ...

What that produces

Two requests, one using each style:

# GET /search/ and GET /checkout/

myproject.view.get.myproject.views.checkout.hit
myproject.view.get.myproject.views.checkout.payment.attempt
myproject.view.get.myproject.views.checkout.payment.authorise
myproject.view.get.myproject.views.checkout.process_request
myproject.view.get.myproject.views.checkout.process_response
myproject.view.get.myproject.views.checkout.process_view
myproject.view.get.myproject.views.checkout.total
myproject.view.get.myproject.views.search.build_queryset
myproject.view.get.myproject.views.search.hit
myproject.view.get.myproject.views.search.json.dumps
myproject.view.get.myproject.views.search.process_request
myproject.view.get.myproject.views.search.process_response
myproject.view.get.myproject.views.search.process_view
myproject.view.get.myproject.views.search.total
myproject.view.http_codes.2xx
myproject.view.http_codes.hit
myproject.view.site.hit

Both names land inside the view that was running: search.build_queryset and checkout.payment.authorise. That nesting is the point. The same helper called from two views gives you two series, so you can see that payment.authorise is slow from checkout and fine everywhere else.

payment.attempt sits alongside as a counter, and search.json.dumps appears without anyone asking for it, because Patched libraries times the stdlib json module.

A timer you start and never stop is a bug, and STATSD_DEBUG makes django-statsd warn about it. It defaults to your DEBUG setting, so you’re probably already getting the warnings where you want them.