The commit phase of enableSharding is currently implemented by ShardingCatalogManager::createDatabase() and includes logic to:

• perform initial checks on the received parameters
• validate that the incoming request does not conflict with already persisted namespaces
• perform the needed insertions into the sharding catalog

Some very similar logic is also implemented within ShardingCatalogManager::addShard() to import the set of databases stored in the shard being added.

A common function could be extracted to remove duplicated code.