The shard key is either a single indexed field or multiple fields covered by a compound index that determines the distribution of the collection’s documents among the cluster’s shards. … Each range is associated with a chunk, and MongoDB attempts to distribute chunks evenly among the shards in the cluster.

What is a good shard key?

The ideal shard key distributes data evenly across the sharded cluster while also facilitating common query patterns. … In a sharded cluster, the mongos routes queries to only the shards that contain the relevant data if the queries contain the shard key.

What is MongoDB shard?

A shard is a single MongoDB instance that holds a subset of the sharded data. Shards can be deployed as replica sets to increase availability and provide redundancy. The combination of multiple shards creates a complete data set.