Backend & systems·Data modelling and storage engines
one database stopped being enough, so you split the rows across several of them and now every query has to know which one to ask.
Sharding
Also calledhorizontal sharding
Splitting data across independent database instances so writes and storage scale past one machine. It is the point at which cross-shard joins, distributed transactions and global uniqueness stop being free. Resharding a live system is one of the hardest routine operations in backend engineering, which is why the shard key deserves more thought than the schema.