In SERVER-15994, the listIndexes, listCollections, and listDatabases commands began requiring the slaveOk bit if the server is a secondary. This was particularly surprising in the case of listDatabases, since the command is many years old, and it broke PyMongo's database_names helper method via direct connection to a secondary (PYTHON-921).

All drivers should check that they set the slaveOk bit when calling any of these three commands if they are directly connected to a mongod. That is, set the bit unless the client is connected to a replica set or a mongos.

Drivers implementing the Server Selection Spec already act this way, but legacy implementations need to be validated.