Large distributed systems run into a problem which smaller systems donâ€™t usually have to worry about. â€œ Brewers CAP Theorem â€ [ Ref 1 ] [ Ref 2 ] [ Ref 3 ] defines this problem in a very simple way. It states, that though its desirable to have Consistency, High-Availability and Partition-tolerance in every system, unfortunately no system can achieve all three at the same time . C onsistent : A fully Consistent system is one where the system can guarantee that once you store a state (lets say â€œx=yâ€) in the system, it will report the same state in every subsequent operation until the state is explicitly changed by something outside the system. [ Example 1 ] A single MySQL database instance is automatically fully consistent since there is only one node keeping the state. [ Example 2 ] If two MySQL servers are involved, and if the system is designed in such a way that all keys starting â€œaâ€ to â€œmâ€ is kept on server 1, and keys â€œnâ€ to â€œzâ€ are kept on server
Thanks for posting this.