Indexing Strategies — Azure DocumentDB

Companion skill to documentdb-query-optimizer. That skill answers "why is this query slow?"; this one answers "which index should I create, and what shape should it take?".

Azure DocumentDB supports the standard MongoDB index types. Only _id is created automatically — every other index must be created explicitly. Default limit: 64 single-field indexes per collection (extendable to 300 on request).

Index engine types

_id vs regular indexes: The _id index is a B-tree, created automatically, and cannot be dropped. For sharded collections the _id key is composite — it includes a hash of the shard key. All other indexes created via createIndex are RUM indexes; the exception is geospatial indexes (2dsphere, 2d), which are GiST indexes.

Rules