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Comment by JulianMorrison | Hacker News Reader

I wish Ryan King had said why the other DBs named were rejected. That could be useful info.

This was actually previously discussed by Twitter's Evan Weaver. I can't find the article I'm thinking of, but this is close: http://blog.evanweaver.com/articles/2009/07/06/up-and-runnin...

My understanding is that it came down to Cassandra being the only one that was well tested in multi-datacenter configurations. I think there were other reasons, but that was the big one.

Sites similar to twitter are worried about Read/Writes and up time rather than concurrency and locking mechanisms. All flavors of NOSQL databases are best suited for this. Sites like amazon.com, or any transaction processing site can't think of using NOSQL. tl:dr; NOSQL is good until transaction processing & concurrency comes in to picture.

Scalaris (http://code.google.com/p/scalaris/) is consistent and has transactions.

As an aside, three sentences doesn't really warrant a "tl;dr".

Not being snarky here but how can anyone seriously consider Scalaris for any data that's even remotely important?

http://code.google.com/p/scalaris/wiki/FAQ#Is_the_store_pers...?

It certainly limits it from being useful if you don't have dollars to throw at high-end infrastructure, but it's not quite as terrible as it sounds. Effectively all it means is that you can't cold start it. How big a problem this is depends like anything else on the application in question.

As I write this comment I just know that in 5 years I will look at it and chuckle at myself but... it boggles my mind to consider a pure-RAM system that relies on at least one copy of the dataset being available forever in some system's "memory grid".

http://highscalability.com/are-cloud-based-memory-architectu...

Amazon pioneered Dynamo, a NoSQL-style scalable distributed key-value store, for building many of their site's internal services upon. It's backed by BDB and can be tuned to guarantee disk writes across multiple nodes if needed. See the paper below.

http://www.allthingsdistributed.com/2007/10/amazons_dynamo.h...

MongoDB does implicit transactions around single queries/commands on single documents, that can be complex enough to be used to create always-recoverable or always-resumable protocols.

It doesn't take a _whole_ lot of familiarity with the other systems to see which of his criteria they failed.

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