Might use this for guidance: https://wiki.10gen.com/display/10GEN/Driver+Exception+Hierarchy

This is what the Ruby Exception hierarchy looks like:

Exception

• NoMemoryError
• ScriptError
  • LoadError
  • NotImplementedError
  • SyntaxError
• SignalException
  • Interrupt
• StandardError
  • ArgumentError
  • IOError
    • EOFError
  • IndexError
  • LocalJumpError
  • NameError
    • NoMethodError
  • RangeError
    • FloatDomainError
  • RegexpError
  • RuntimeError
  • SecurityError
  • SystemCallError
  • SystemStackError
  • ThreadError
  • TypeError
  • ZeroDivisionError

SystemExit
fatal

Proposed Hierarchy (from wiki):

MongoException

• MongoDriverException
  • MongoSocketException
    • MongoSocketReadTimeoutException
    • MongoSocketWriteTimeoutException
    • MongoConnectionException
  • MongoProtocolException
• MongoOperationException
  • MongoAuthenticationException
  • MongoWriteConcernException
    • MongoDuplicateKeyException
    • MongoNotMasterException
    • MongoWTimeoutException
  • MongoQueryException
    • MongoQueryTimeoutException (for $maxTime, when available)
    • MongoCursorNotFoundException
  • MongoMultipleException (for mongos)