Speed is a feature

A mystical journey through Django performance optimization techniques, tools and gotchas.

Talk presented at Django Meetup Buenos Aires June 2014

Transcript

1. This slide was intentionally left blank
2. Speed is a feature A mystical journey through Django performance optimization techniques, tools and gotchas
3. Roadmap How to find performance problems Sneak peak: Front-end performance How to fix them in Django
4. Why? [Google] found that Half a second delay caused a 20% drop in traffic. [Amazon] found that even very small delays would result in substantial and costly drops in revenue. Users really respond to speed 2006
5. There’s nothing like data Don’t start with the code. Profile and gather real usage data.
6. There’s nothing like real data Identify bottlenecks New Relic Paid service Very good Google Analytics Free of charge Less detail Your logs No data to third parties Harder to use Profiling Complex setup required Overhead
7. New Relic
8. New Relic
9. Google Analytics Site Speed
10. There’s nothing like data Let’s find the culprit! django-debug-toolbar django-debug-toolbar-template-timings
11. Time all the things!
12. Typical backend bottlenecks Database External Services CPU Intensive task Template Rendering
13. Database Missing index select_related() prefetch_related() Order
14. select_related() >>> for c in Comment.objects.all(): print c.user.name # select * from comments; # select * from users where id = 1; # select * from users where id = 2; ... >>> comments = Comment.objects.all(); >>> for c in comments.select_related(“user”): print c.user.name # select comments.*, users.* # from comments, users # where comments.user_id = users.id;
15. prefech_related() >>> for u in User.objects.filter(id__lt=10): print len(u.comments.all()) # select * from users; # select * from comments where user_id = 1; ... >>> users = User.objects.filter(id__lt=10) >>> for u in users.prefetch_related(“comments”): print len(u.comments.all()) # select * from users where id < 10; # select * from comments # where user_id in (1,2,3,4,5,6,7,8,9); ## Joins them in python
16. Background Jobs Celery from celery import task @task def send_confirmation_email(user_id): ... def login(req): ... send_confirmation_email.delay(req.user.id) return HttpResponseRedirect(“/home/”)
17. Caching! DB External Services CPU intensive tasks
18. Caching! Per view cache from django.views.decorators.cache import cache_page @cache_page(60 * 15) # seconds def my_view(request): ...
19. Caching! Low level cache API >>> from django.core.cache import get_cache >>> cache = get_cache('default') >>> cache.set('my_key', 'hello, world!', 30) >>> cache.get('my_key') >>> from django.core.cache import caches >>> cache = caches['default']
20. Caching! from django.core.cache import get_cache cache = get_cache('default') def last_comments(request): comments_ids = cache.get('last_comments') if comments_ids: comments = Comment.objects.filter(id__in=comments_ids) else: comments = fetch_last_comments() comments_ids = [c.id for c in comments] cache.set('last_comments', comments_ids) ... Low level cache API
21. Caching! Django Cacheback from cacheback.decorators import cacheback @cacheback def fetch_last_comments_ids(): ... def last_comments(request): comments_ids = fetch_last_comments_ids() comments = Comment.objects.filter(id__in=comments_ids) ...
22. Template Compilation Use django.template.loaders.cached.Loader TEMPLATE_LOADERS = ( ('django.template.loaders.cached.Loader', ( 'django.template.loaders.filesystem.Loader', 'django.template.loaders.app_directories.Loader', )), )
23. Template Fragment Caching {% load cache %} {% cache 500 “last_comments” %} .. last comments .. {% endcache %} {% load cache %} {% cache 500 “my_recent_comments” user.id %} .. user’s recent comments .. {% endcache %}
24. Don’t forget about the browser 80% or more of the end-user response time is spent in the front end Combine Compress Cache Less is more Load slow things later Focus on making the important things faster
25. Don’t forget about the browser Google PageSpeed Insights webpagetest.org Chrome & Firefox
26. Assets Django Compressor {% compress js %} <script src="/static/js/one.js"></script> <script>obj.value = "value";</script> {% endcompress %} Django Assets {% assets "js_all" %} <script async src="{{ ASSET_URL }}"></script> {% endassets %}
27. Q & Maybe A @polmuz
28. References Gist with all the links - http://bit.ly/1mV5Z0W Performance is a feature - http://blog.codinghorror.com/performance-is-a-feature/ Marissa Mayer at Web 2.0 - http://glinden.blogspot.com.ar/2006/11/marissa-mayer-at-web-20.html Psychology of Web Performance - http://www.websiteoptimization.com/speed/tweak/psychology-web-performance/ New Relic - http://newrelic.com Google Analytics - http://www.google.com/analytics/ Tracking Application Response Time with Nginx - http://lincolnloop.com/blog/tracking-application-response-time-nginx/ Logging Apache response times - http://www.moeding.net/archives/33-Logging-Apache-response-times.html Django Debug Toolbar - http://django-debug-toolbar.readthedocs.org/ DDT Template Timings - https://github.com/orf/django-debug-toolbar-template-timings Django Database Optimizations - https://docs.djangoproject.com/en/1.7/topics/db/optimization/ Two Hard Things - http://martinfowler.com/bliki/TwoHardThings.html Django Cache Docs - https://docs.djangoproject.com/en/1.7/topics/cache/ Django Cacheback - http://django-cacheback.readthedocs.org/en/latest/index.html Cached Templates - https://docs.djangoproject.com/en/1.7/ref/templates/api/#django.template.loaders.cached.Loader Google PageSpeed Insights - https://developers.google.com/speed/pagespeed/insights/ Web Page Test - http://www.webpagetest.org/ Django Compressor - http://django-compressor.readthedocs.org/en/1.3/ Django Assets - http://django-assets.readthedocs.org/en/0.8/