Description

Unique indexes on sharded collections can only be enforced on the shard key or a prefix of the shard key.

The Behaviour section of the Unique Index page mentions building unique indexes on replica sets and sharded clusters: https://docs.mongodb.com/manual/core/index-unique/#building-unique-index-on-replica-sets-and-sharded-clusters.

However, the caveats for unique indexes in sharded clusters are a fair distance down the page: https://docs.mongodb.com/manual/core/index-unique/#sharded-clusters-and-unique-indexes.

These two behaviour notes should be adjacent for context.

Scope of changes

Impact to Other Docs

MVP (Work and Date)

Resources (Scope or Design Docs, Invision, etc.)