Perl doesn't have "garbage collection" in the sense that it never gives memory back to the OS.
in reply to Timing of garbage collection
Once Perl has memory from the OS, it has it forever.
A long-lived Perl app will reach a maximum memory usage and just stay at that number forever (provided no memory leaks).
If you un-define an object ref: $obj_a = undef;
$obj_a = Method_X->new(...), reuse/reassign an object ref that has the same effect as long as no reference to an in internal structure within obj_a is in existence.
Perl has its own memory management and reuses memory when it can.