Improving mod_perl Driven Site's Performance -- Part III: Code Profiling and Memory Measurement Techniques Page 5

  PerlSetVar StatusOptionsAll On
  PerlSetVar StatusTerse On
  PerlSetVar StatusTerseSize On
  PerlSetVar StatusTerseSizeMainSummary On

  PerlModule B::TerseSize

Now you can start to optimize your code. Or test which of the several implementations is of the least size.

For example, let's compare CGI.pm's OO vs. procedural interfaces:

As you will see below the first OO script uses about 2k bytes while the second script (procedural interface) uses about 5k.

Here are the code examples and the numbers:

1. 
   

     cgi_oo.pl
     ---------
     use CGI ();
     my  = CGI->new;
     print ->header;
     print ->b("Hello");
   
   
   
     cgi_mtd.pl
     ---------
     use CGI qw(header b);
     print header();
     print b("Hello");
   

After executing each script in single server mode (-X) the results are:

1.   Totals: 1966 bytes | 27 OPs
   
     handler 1514 bytes | 27 OPs
     exit     116 bytes |  0 OPs

2.   Totals: 4710 bytes | 19 OPs
   
     handler  1117 bytes | 19 OPs
     basefont  120 bytes |  0 OPs
     frameset  120 bytes |  0 OPs
     caption   119 bytes |  0 OPs
     applet    118 bytes |  0 OPs
     script    118 bytes |  0 OPs
     ilayer    118 bytes |  0 OPs
     header    118 bytes |  0 OPs
     strike    118 bytes |  0 OPs
     layer     117 bytes |  0 OPs
     table     117 bytes |  0 OPs
     frame     117 bytes |  0 OPs
     style     117 bytes |  0 OPs
     Param     117 bytes |  0 OPs
     small     117 bytes |  0 OPs
     embed     117 bytes |  0 OPs
     font      116 bytes |  0 OPs
     span      116 bytes |  0 OPs
     exit      116 bytes |  0 OPs
     big       115 bytes |  0 OPs
     div       115 bytes |  0 OPs
     sup       115 bytes |  0 OPs
     Sub       115 bytes |  0 OPs
     TR        114 bytes |  0 OPs
     td        114 bytes |  0 OPs
     Tr        114 bytes |  0 OPs
     th        114 bytes |  0 OPs
     b         113 bytes |  0 OPs

Note, that the above is correct if you didn't precompile all CGI.pm's methods at server startup. Since if you did, the procedural interface in the second test will take up to 18k and not 5k as we saw. That's because the whole of CGI.pm's namespace is inherited and it already has all its methods compiled, so it doesn't really matter whether you attempt to import only the symbols that you need. So if you have:

  use CGI  qw(-compile :all);

in the server startup script. Having:

  use CGI qw(header);

or

  use CGI qw(:all);

is essentially the same. You will have all the symbols precompiled at startup imported even if you ask for only one symbol. It seems to me like a bug, but probably that's how CGI.pm works.

BTW, you can check the number of opcodes in the code by a simple command line run. For example, comparing 'my %hash' vs. 'my %hash = ()'.