It's probably easier to just add something else to your
primary key than to try and get sub-second responses. A
good example is to use:
$mykey = "$^T$$";
which sets the key to a combination of the time
in seconds and the process ID. This combination
will be unique, as long as each time the script is
run it generates a single key (e.g. a web script).
If the script generates more than one key per second,
add a counter:
$mykey = "$^T$$" . $x++;
If you do need sub-second times, you can look
at the Time::HiRes module, although it may not
work on your system, as it uses syscall
and gettimeofday(2)
in C. Probably easier overall to use the
technique above.
