Db tips & tricks django meetup

Tips & Tricks Making Django play nice with your database

Save your changes No really, make sure they’re actually saved • save() isn’t thread safe • update() works pretty well • and is amazing for race conditions • and counters

Atomic UPDATEs Atomic updates are great for thread safety

Atomic UPDATEs But we didn’t want to keep typing that out

QuerySets are heavy • no identity mapper, duplicate rows • django-idmapper can help • instance creation is costly • selects and joins are unoptimized • joins dont scale

Partition your queries Joins don’t scale, and are costly...

Partition your queries ... and so are keystrokes

Caching is bad? QuerySet caching is nice, but not always wanted

Instances are expensive Not all instances, mostly Django models • Reddit comment model -- we pulled all objects into memory • Creation of thousands of instances when we only need a small number

Instances are expensive Here’s what we mean Optimized to delay instance creation

Instances are expensive Delaying creation until it was needed 700 µs Average process time 525 µs 350 µs 175 µs 0 µs 800 25 Initial instances created We didn’t even measure memory costs (and yes, this chart IS useless)

Thanks David Cramer @zeeg david@disqus.com http://www.davidcramer.net P.S. we’re hiring kickass Django engineers (and some frontend guys too)

References & Stuff • django-idmapper http://github.com/dcramer/django-idmapper • instance.update() http://gist.github.com/550436 • attach_foreignkey http://gist.github.com/550435 • SkinnyQuerySet http://gist.github.com/550438

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Db tips & tricks django meetup

by zeeg on Aug 25, 2010

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