The aim of this ticket is to reduce the error-prone code on sharding DDL coordinators by avoiding keeping references to the _doc attribute, which is very likely to get freed while a reference is taken.

This is a list of some of the places where we take and keep references to _doc:

• ShardingDDLCoordinator::nss() when namespace is time-series
• DropDatabaseCoordinator::_runImpl
• DropDatabaseCoordinator::_dbName attribute
• RenameCollectionCoordinator::renameIndexMetadataInShards