Sleep is woken by signals. Perhaps some are being used by the database driver. Just keep going back to sleep until you want to wake up.

# Optional, but a good idea with short durations.
use Time::HiRes qw( sleep time );

sub uninterrupted_sleep {
   my ($duration) = @_;
   die if !$duration;
   my $sleep_till = time() + $duration;
   while ($duration > 0) {
      sleep($duration);
      $duration = $sleep_till - time();
   }
}
[download]