Details of "show slave/master status"

[Mark Arnold]

Hi,

can somebody point me to a documentation of the columns that "Show slave status"
and "show master status" returns? What are the different Relay-Log-Pos values?
Which of those values should I consider if I want to write a monitoring-script that sends out alerts if the replication starts to stall/fail/get problems? What are acceptable numbers and when does it start to become critical?

Also, when I use "show slave hosts" on the master (version 4.1.11-standard-log) , I get no result, although the "show slave status" on the slave claims that everything is fine...

Any kind of help or pointer would be appreciated.

Thanks,

MARK