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Craig Kerstiens

Category: Django

Fixing Database Connections in Django

If you’re looking to get better performance from your Django apps you can check out Pro Django, PostgreSQL High Performance, or read some my earlier posts on Postgres Performance. All of these are of course good things to do – you can also start by correcting an incredibly common but also painful performance issue, that until 1.6 is unaddressed in Django.

Django’s current default behavior is to establish a connection for each request within a Django application. In many cases any particularly in distributed cloud environments this is a large time sink of your response time. An example application running on Heroku shows a typical connection time of 70ms. A large part of this time is the SSL negotiation that occurs in connecting to your database, which is a good practice to ensure security of your data. Regardless, this is a long time in simply establishing a connection. As a point of comparisson its commonly encourage that most queries to your database are under 10ms.

An example that highlights this in a small lightweight application shows the bulk of a request time being within a connection displayed by New Relic:

connection time

Introducing django-db-tools

For any successful web application there is likely to come a time when you need to conduct some large migration on the backend. I dont mean simple add a column here or add an index there, but rather truly sizeable migrations… Going from MySQL to Postgres or migrating from an older version of Postgres such as a 32 bit instance to a newer 64 bit instance. In these cases the default approach is to just schedule downtime often throwing up a splash screen saying so.

For many sites this approach is simply wrong and lazy, with little effort you can improve the experience and there by ease the burden in conducting these types of migrations. By having the ability to turn your site into a read only mode which Simon Wilson talked about in his post on Lanyrd you can still continue to operate just in a limited capacity. Andrew Godwin further talks about some of this as well in regards to the Lanyrd move and even includes the script they used to migrate data from MySQL to Postgres. Though just in talking with Simon about this a week ago it occurred to me they had not released the code for their read-only mode.

Finally onto the announcing, today I’m releasing django-db-tools. This is currently a very lightweight utility that allows you to flip your site into two modes.

Using Postgres Arrays in Django

A few weeks back I did a brief feature highlight on Postgres arrays. Since that time I’ve found myself using them with increasing regularity on small side projects. Much of this time I’m using Django and of course not opting to write raw SQL to be able to use arrays. Django actually makes it quite simple to work with Arrays in Postgres with a package by Andrey Antukh. Lets get started by installing two libraries:

Schemaless Postgres in Django

Earlier this week while I was at DjangoCon EU there seemed to be a surprising amount of talk about MongoDB. My problem with this isn’t with MongoDB, but in the assumption that only Mongo can solve what you’re looking for. By and far the most common feature is people want schemaless. It gives them flexibility in their data model and lets them iterate quickly. While I still opt for relational models that map cleanly to a relational database, there are cases where developers may want schemaless.

Apps to Services

Update the talk for this is now viewable on YouTube here When I first came across Django I was an immediate fan. It featured: Good documentation Steady but stable progress Community around apps which encouraged DRY I’ve been a user off and on depending on my needs for nearly four years since discovering it, and throughout that time all of the above have remained true. However, as I’ve worked on and encountered more complex applications there’s one thing that has time and again broke down for me, which is the Django apps model.

Getting Started with Django

For those completely new to web development, Django is a web framework that makes it easier to build web applications with Python. For those that have some knowledge of other web frameworks and Django you may be able to fly through much of the following. Django is a slight modification on the MVC construct which views itself as a MVT Model, View, Template. Django views a website as a project and within it smaller apps are contained.

Environment Structure for Django Apps

I’ve been writing applications off and on for nearly 4 years now, since before Django 1.0 was even released. I must say the framework could not be better described than by its own tagline “The Web framework for perfectionists with deadlines”. Among the things I love about it are:

JQuery and Django Autocomplete

In a couple of various places I’ve seen light requests of how to put autocomplete in for a Django web application. Here’s a really light weight version with a view and autocomplete functionality using: from django.utils import simplejson def autocompleteModel(request): search_qs = ModelName.objects.filter(name__startswith=request.REQUEST['search']) results = [] for r in search_qs: results.append( resp = request.REQUEST['callback'] + '(' + simplejson.dumps(result) + ');' return HttpResponse(resp, content_type='application/json') For the jQuery autocomplete and call: