Sharding has become a popular means of achieving scalability in application architectures in which read/write data separation is not only possible, but desirable to achieve new heights of concurrency. The premise is that by splitting up read and write duties, it is possible to get better overall performance at the cost of a slight delay in consistency. That is, it takes a bit of time to replicate changes initiated by a «write» to the read-only master database. It’s eventually consistent, and it’s generally considered an acceptable trade off when searching for higher and higher scalability.