Tez Counter question

[Joe Zhang (SDE)]

HI Tez experts:

Now I am using Tez Rest API to get tez tasks running Info, but I am confusing 
some concepts in Counter

<1>  For File system counters:

counterName : FILE_BYTES_READ ? does it mean read from local disk or somewhere 
else ?

                                     HDFS_BYTES_READ ?  is it included by 
FILE_BYTES_READ ?

<2>  For org.apache.tez.common.counters.TaskCounter:

counterName SHUFFLE_BYTES ? does it have some relationship with FILE_BYTES_READ 
? which data should be included in it ?

Best wishes
Joe zhang