MongoDB Administrator's Guide

Choosing the shard key

In order to partition data across multiple shards, MongoDB uses a shard key. This is an immutable key that can be used to identify a document within a sharded collection. Based on boundaries of the shard key, the data is then divided into chunks and spread across multiple shards within a cluster. It is important to note that MongoDB provides sharding at the collection level and a sharded collection can have only one shard key. As shard keys are immutable, we cannot change a key once it is set. It is extremely important to properly plan shard keys before setting up a sharded cluster.

MongoDB provides two sharding strategies—a hashed shard key and ranged shard key.

In hashed shard keys, MongoDB computes and indexes on ...