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Speed is a featureA mystical journey through Django performance optimization techniques, tools and gotchas

Roadmap

How to find performance problems

Sneak peak: Front-end performance

How to fix them in Django

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 speed2006

There’s nothing like data

Don’t start with the code. Profile and gather real usage data.

There’s nothing like real data

Identify bottlenecks

New Relic

Paid serviceVery good

Google Analytics

Free of chargeLess detail

Your logs

No data to third partiesHarder to use

Profiling

Complex setup requiredOverhead

New Relic

New Relic

Google Analytics Site Speed

There’s nothing like data

Let’s find the culprit!

django-debug-toolbar

django-debug-toolbar-template-timings

Time all the things!

Typical backend bottlenecks

Database

External Services

CPU Intensive task

Template Rendering

Database

Missing index

select_related()

prefetch_related()

Order

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;

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

Background Jobs

Celery

from celery import task

@taskdef send_confirmation_email(user_id): ...

def login(req): ... send_confirmation_email.delay(req.user.id) return HttpResponseRedirect(“/home/”)

Caching!

DBExternal Services

CPU intensive tasks

Caching!

Per view cache

from django.views.decorators.cache import cache_page

@cache_page(60 * 15) # secondsdef my_view(request): ...

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']

Caching!

from django.core.cache import get_cachecache = 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

Caching!

Django Cacheback

from cacheback.decorators import cacheback

@cachebackdef fetch_last_comments_ids():

...

def last_comments(request):comments_ids = fetch_last_comments_ids()comments = Comment.objects.filter(id__in=comments_ids)

...

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',

)),

)

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 %}

Don’t forget about the browser

80% or more of the end-user response time is spent in the front end

CombineCompress

CacheLess is more

Load slow things laterFocus on making the

important things faster

Don’t forget about the browser

Google PageSpeed Insights

webpagetest.org

Chrome & Firefox

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 %}

Q & Maybe A

@polmuz

ReferencesPerformance 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/