relational databases and multicast messages

Question

I have read that relational databases are a terrible way to do multicast messages like twitter.

So twitter saves every tweet only one times and then retrieve its in every stream ? or saves every tweet in every users's stream ?

I want to know why relational database ( like mysql or postgresql ) doesn't good for twitter-like application.

Answer 1

It really depends on your application. NoSQL, a column-based database or Relational database will both scale differently depending upon your design and requirements. And large sites like Twitter do a lot of caching.

Don't prematurely optimize. Write your application and profile it. 80% of your slowness will be in 20% of your code/queries.