Db tips & tricks django meetup
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  • 1. Tips & Tricks Making Django play nice with your database
  • 2. 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
  • 3. Atomic UPDATEs Atomic updates are great for thread safety
  • 4. Atomic UPDATEs But we didn’t want to keep typing that out
  • 5. QuerySets are heavy • no identity mapper, duplicate rows • django-idmapper can help • instance creation is costly • selects and joins are unoptimized • joins dont scale
  • 6. Partition your queries Joins don’t scale, and are costly...
  • 7. Partition your queries ... and so are keystrokes
  • 8. Caching is bad? QuerySet caching is nice, but not always wanted
  • 9. 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
  • 10. Instances are expensive Here’s what we mean Optimized to delay instance creation
  • 11. 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)
  • 12. Thanks David Cramer @zeeg david@disqus.com http://www.davidcramer.net P.S. we’re hiring kickass Django engineers (and some frontend guys too)
  • 13. 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