is createIndexes in mongoose idempotent?

[kasir-barati]

In MongoDB API it seems like calling this API is basically safe as many times as you like since it is idempotent: https://www.mongodb.com/community/forums/t/behavior-of-createindex-for-an-existing-index/2248

But I just wanna confirm that this is also the case for DocumentDB in AWS.

And whether it will try to reindex the existing document again and again if I call this API on a collection with lots of documents.

[kasir-barati]

A related question: #15462 (comment)

[vkarpov15]

I believe so, but Mongoose doesn't officially support DocumentDB or test against DocumentDB so I'm not certain.

[Sumit-Mayani]

Yes, createIndexes() in Mongoose is idempotent.

Under the hood, Mongoose calls MongoDB's createIndex for each index defined in your schema. MongoDB's createIndex is idempotent — if an index already exists with the same key and options, MongoDB returns successfully without recreating it or re-indexing the collection.

Regarding re-indexing: MongoDB does not re-index existing documents when you call createIndexes and the index already exists. Documents are only indexed when an index is newly created.

Regarding AWS DocumentDB: DocumentDB is MongoDB-compatible and also treats createIndex as idempotent for indexes with the same specification. It will not duplicate or re-index on repeated calls. That said, always verify against your specific DocumentDB version since it lags behind MongoDB feature parity.

Best practice: It is safe to call createIndexes() on every app startup (which Mongoose does automatically when autoIndex: true, the default). On subsequent restarts, MongoDB/DocumentDB will skip indexes that already exist, so there is no performance penalty on large collections.