Showing posts from February 21, 2010

Eventual consistency is just caching ?

So there is someone who thinks “ eventual consistency is just caching ”.  Though I liked the idea of discussing this, I don’t agree with Udi’s views on this. “Cache” is generally used to store data which is more expensive to obtain from the primary location. For example, caching mysql queries is ideal for queries which could take more than fraction of a second to execute. Another example is caching queries to S3, SimpleDB or Google’s datastore which could cost money and introduce network latency into the mix. Though most applications are built to use such caches, they are also designed to be responsive in absence of caching layer. The most important difference between “cache” and a “datastore” is that the dataflow is generally from “datastore” to “cache” rather than the other way round. Though one could queue data on “cache” first and then update datastore later (for performance reasons) that is not the way one should use it. If you are using “ca