Search notes:

oradebug dyn_gcr

Usage are: 
oradebug dyn_gcr -m metric_index -enable/-disable [-force]
oradebug dyn_gcr -a action_index -enable/-disable
oradebug dyn_gcr -all -m
oradebug dyn_gcr -all -a
oradebug dyn_gcr -freq metric_index frequency(in secs)

See also

oradebug

Index