Comment by mackwic | Hacker News Reader

Comment by mackwic | Hacker News Reader

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It's not about performance and bottlenecks, it's about CAP theorem: any system can provide only 2 of either Consistency, Availability, or Partition-tolerant.

Consistency: you want all you cluster to have the same data.

Availability: you want being able to lose one node or more in case of some issue.

Partition-tolerant: in case of net-split (think IRC), the splitted part of your cluster can work in isolation, then re-heal when the link is up again.

When someone sell you auto-healing and cluster reliability, they are selling you AP, which means that you lose the C, something we all takes for granted. Cassandra is one of those. Think of what you can't do when all your nodes can have different data of the same model.

Sorry for the useless explanation if you already knew that.

>When someone sell you auto-healing and cluster reliability, they are selling you AP, which means that you lose the C, something we all takes for granted. Cassandra is one of those. Think of what you can't do when all your nodes can have different data of the same model.

This is pretty hyperbolic. Netflix does perfectly fine with this model given that they run Cassandra at its lowest consistency level[1]. If they can reliably store watch histories, run recommendations, settings, and playlists on this model well I'm wondering what you have in mind when you say "think of what you can't do". Besides, its not like large AP systems are a new thing, have you ever overdrawn your account?

[1] http://planetcassandra.org/blog/a-netflix-experiment-eventua...

This is the most hand-wavy, unrigorous talk on a distributed database I've ever seen. You run a test 5 times in optimistic conditions and that gives you confidence that "you can trust it" to replicate your writes?

There are a multitude of failure cases in which it cannot replicate those writes. Ultimately your database has to be a decision based on the availability and consistency needs due to your use case, period. "Trust" should never come into the discussion at all, you should be well aware of what your tradeoffs mean in the worst case.

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