Think looping

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Here is a simple sample taken from a (much) bigger project:

sub write_status {   my $self = shift;   my $statustext = shift;
   my $sth = $self->{dbh}->prepare_cached('UPDATE STATUS SET text=? WHERE id=?');   $sth->execute($statustext, $self->{job_id});   $sth->finish; # Required in older DBD::mysql versions due to a bug}
sub write_protocol {   my $self = shift;   my $item_id = shift;   my $action = shift;
   open my $log_fh,'>>', $self->{protocol_file} or return;   print $log_fh join("\t", time, $action, $item_id)."\n";   close $log_fh;}

for my $no (0..$#items) {   $self->write_status($no / $#items);   $self->write_protocol($items[$no]->id, 'something');   [...]}

The issue was raised when a customer couldn't be serviced because the processing took 24 hours on a busy system. Only few lines are necessary to improve the runtime:

sub write_status {   my $self = shift;   my $statustext = shift;
   # Don't flush two status reports within one second   return if $self->{last_status} and $self->{last_status} == time;
   my $sth = $self->{dbh}->prepare_cached('UPDATE STATUS SET text=? WHERE id=?');   $sth->execute($statustext, $self->{job_id});   $sth->finish; # Required in older DBD::mysql versions due to a bug
   $self->{last_status} = time; # Note the time of the last second}
sub write_protocol {   my $self = shift;   my $item_id = shift;   my $action = shift;
   # Cache the filehandle within the object   my $log_fh = $self->{protocol_fh}; # print $self->{protocol_fh} $content won't work   if (!$log_fh) {      open $log_fh,'>>', $self->{protocol_file};      $self->{protocol_fh} = $log_fh;   }   return unless $log_fh;
   print $log_fh join("\t", time, $action, $item_id)."\n";   close $log_fh;}

The results: prepare_cached completely left the top15 time consuming function calls in NYTProf profiling and only one third of all $sth->execute calls survived the changes. The overall process time was cut by half with that few changed lines.

Try not only the write straightforward sourcecode but also try to think about how often the source is called and if parts could be re-used in the same run.