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Reddit in fact now runs on Cassandra - the top nosql solution for a social website

That's interesting. The guys at reddit previously compared various database systems including Amazon's SimpleDB, and found that PostgreSQL was the fastest (see 'Scaling your Python application on EC2' from PyCon 2010: http://pycon.blip.tv/file/3257303/ )

Appearently Reddit switched over to Cassandra in March 2010 (http://blog.reddit.com/2010/03/she-who-entangles-men.html)

To clarify, Reddit replaced memcachedb w/ cassandra entirely, but a lot of the site is still on postgresql. My understanding is they plan to move more to Cassnadra gradually.

Shouldn't lots of redundancy be a fundamental part of which ever db you are using.

As to extreme do-normalization, colour me sceptical, why not parallelise and throw more hardware at the problem?

Because it's more cost effective to de-normalize then to parallelise in this instance.

Turns out it's difficult to parallelize without also denormalizing...

*schema