Sharding
Also called: Horizontal partitioning, Partitioning
Splitting one big database into several smaller ones, each holding part of the data.
Definition
When data or traffic outgrows one database server, you split it by a shard key: each shard holds the rows whose key maps to it, often by hashing the key. Lookups by that key go to exactly one shard. Queries that don't use the key have to ask every shard, so choosing the key is the most important decision.
In practice
A URL shortener shards by short code, so every redirect reads from exactly one shard.
Learn it in context
Lessons that use this term.