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Comment by narrator | Hacker News Reader

Reddit runs on Cassandra + PostgreSQL. They use Cassandra as a key/value store and not as the primary database though.

They are planning to transition to Cassandra as the primary database. PostgreSQL is not used in a relational way on reddit -- it is used as a makeshift k-v store. You can take a look at this yourself as reddit is fully open-source: http://github.com/reddit .

> They are planning to transition to Cassandra as the primary database.

do you have a source for that ?

> it is used as a makeshift k-v store

That is very true, they should switch. It just seemed like they had no plan to do so.

I could swear an admin said it with some pretty fair definitiveness; I thought I remembered that it was ketralnis, but this was the best I could find from him, and it's not nearly as definite as my memory says.

http://www.reddit.com/r/programming/comments/bcqhi/reddits_n...

> > They are planning to transition to Cassandra as the primary database.

> do you have a source for that ?

Yes. Me.

According to reddit admins some of the recent downtimes in the last few months were due to cassandra and they were having some bad performance and stability issues. I can look it up if anyone is interested but it will be a bit of a work, since they stated it (several times) in the comment section and perhaps once on a blog post too.

The cassandra issues were primarily ops failures, and secondarily an older version of Cassandra making it difficult to recover once it was overwhelmed. (Some of the resulting improvements in Cassandra are documented here: http://www.riptano.com/blog/whats-new-cassandra-065)

Cassandra looks to be working fine for reddit now: http://blog.reddit.com/2010/08/everything-went-better-than-e...

This could very well be, I remember one of the problems they were having is not having enough resources for cache or something similar. But I could be wrong I will ask them on twitter and see if they can comment here on it.

> Cassandra looks to be working fine for reddit now

Yep

That would be me, and you're misquoting me.

I screwed up our Cassandra deployment, and wrote about how I screwed it up. We were under-provisioned, and the version we were using didn't deal with the case of being overloaded in a graceful way. We're no longer under-provisioned, so I don't know if more recent versions deal with it better.

We've never claimed to have performance issues, I don't know where you're getting that one.

yup faulty memory, I tried to be more clear here: http://news.ycombinator.com/item?id=1670968

No malicious intent, after all, I did ask you for verification on twitter, linking here.

> They use Cassandra as a key/value store and not as the primary database though

These are orthogonal.

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