MISSING SOME STATISTICS DESCRIPTION IN DATABASE REFERENCE

Hi All,
Can some one provide me some documentation on class description for these 4 classes. I can not find any clear document about that.

33
40
72
192

These are the statistics listed under those classes:

STATISTIC#             NAME                                                             CLASS                  
---------------------- ---------------------------------------------------------------- ----------------------
517                    Clusterwide global transactions                                  33                    
518                    Clusterwide global transactions spanning RAC nodes               33                    
519                    Forwarded 2PC commands across RAC nodes                          33                    
117                    DBWR fusion writes                                               40                    
205                    gc cr blocks served                                              40                    
206                    gc cr block flush time                                           40                    
207                    gc read wait time                                                40                    
208                    gc read waits                                                    40                    
209                    gc read wait failures                                            40                    
210                    gc read wait timeouts                                            40                    
211                    gc current blocks served                                         40                    
212                    gc current block pin time                                        40                    
213                    gc current block flush time                                      40                    
214                    gc cr blocks received                                            40                    
215                    gc cr block receive time                                         40