SERVER ticket description: The collection catalog stores metadata for each collection in one document. This includes an array of index specs for indexes belonging to the collection. Each index spec entry contains the 'ns' field, and with the removal of the restriction on collection name length, this has the potential to quickly hit the documents BSON limit.
There is already an 'ns' field at the top-level of the collection metadata document that could be used instead.
Change Description: This ticket removed the 'ns' field from all index specs starting in 4.3. Any commands that retrieve index specifications from MongoDB (such as listIndexes) will be affected and will no longer have the 'ns' field be part of the output.