Django-Cache

Using redis and django-redis to perform caching for the django application

In this tutorial we will be setting up Redis and [Django] using [django-redis] and enable caching for our django web application.

Caching refers to storing the server response in the client itself, so that a client need not make a server request for the same resource again and again. A server response should have information about how caching is to be done, so that a client caches the response for a time period or never caches the server response.

Installation

First of all install Redis from the official website if using linux then install using the below commands or follow the instructions given on the website

# command to install
sudo apt-get install redis-server

# command to run server
redis-server

# command to check if running
redis-cli ping

# output
PONG

Now using pipenv create a virtualenv and install the libraries, if pipenv is not installed then install it using pip

# install pipenv using
pip install pipenv

# command to create virtualenv
pipenv install django django-redis djangorestframework

# command to activate env
pipenv shell

Two new files will be made by pipenv --> Pipfile and Pipfile.lock

Project Setup

start django project

django-admin startproject django_cache .

run migrations and server

python manage.py migrate
python manage.py runserver

start app store

python manage.py startapp store

Configure project settings

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',

    # django apps
    'store',

    # packages
    'rest_framework',
]

To start using django-redis, you should change your Django cache settings to something like this:

CACHES = {
    "default": {
        "BACKEND": "django_redis.cache.RedisCache",
        "LOCATION": "redis://127.0.0.1:6379/1",
        "OPTIONS": {
            "CLIENT_CLASS": "django_redis.client.DefaultClient",
        }
    }
}

Configure as session backend:

SESSION_ENGINE = "django.contrib.sessions.backends.cache"
SESSION_CACHE_ALIAS = "default"

For complete code for django checkout the project files.

loadtest

Install loadtest using npm

npm install -g loadtest

Don't forget to run django server before running loadtest command as well as redis-server:

# run these commands from separate terminals or command prompts
python manage.py runserver
redis-server

Run the below command to test the performance of our application

# command that runs 1000 requests with -k = keep connection alive and the url at last
loadtest -n 1000 -k  http://localhost:8000/store/

# output
INFO Target URL:          http://127.0.0.1:8000/store/
...
INFO Max requests:        1000
...
INFO Completed requests:  100
...
INFO Requests per second: 41
...

Check your terminal for more detailed results from loadtest command.

Cached View

from django.shortcuts import render
from django.core.cache import cache
from django.conf import settings
from django.core.cache.backends.base import DEFAULT_TIMEOUT

from rest_framework.decorators import api_view
from rest_framework.response import Response
from rest_framework import status

from .models import Product

CACHE_TTL = getattr(settings, 'CACHE_TTL', DEFAULT_TIMEOUT)
...

# view for cached products
@api_view(['GET'])
def view_cached_products(request):
	if 'product' in cache:
		products = cache.get('product')
		return Response(data=products, status=status.HTTP_201_CREATED)
	else:
		products = Product.objects.all()
		results = [product.to_json() for product in products]

		# store products in cache
		cache.set('product', results, timeout=CACHE_TTL)
		return Response(data=results, status=status.HTTP_201_CREATED)

The code above will check if the key product is present in the cache, and if found, the data represented will be returned to the browser. In the event that no data is present in the cache, we first retrieve the data from the database, store it in the cache, and then return the data queried to the browser.

Now that we have cached our view we can carry our tests again but this time with cached view.

loadtest -n 1000 -k http://127.0.0.1:8000/store/cache

# increased number of requests per second
INFO Requests per second: 248

The first time you hit the endpoint localhost:8000/store/cache, the application will query from the database and return data, but subsequent calls to the URL will bypass the database and query from the cache since the data is already available in the cache.

You can check if the key 'product' is stored in cache or not by

python manage.py shell

# import cache and get the 'product' key
from django.core.cache import cache
cache.get('product')

# output
[{'name': 'hedphones',
  'description': 'best audio with non blocking IO',
  'price': '49.99',
  'timestamp': '2018-10-17 03:53:56.850768+00:00',
  'updated': '2018-10-17 03:53:56.850768+00:00'}]

Try increasing the number of requests in loadtest and testing out the cached django application.