#!/usr/local/bin/perl -w

use LWP::UserAgent; 
use Crypt::SSLeay; 
use HTTP::Cookies; 
use HTTP::Headers; 
use HTTP::Request; 
use HTTP::Response; 
use Time::HiRes 'time','sleep';

# constants:

$DEBUG       = 0; 
$browser     = 'Mozilla/4.04 [en] (X11; I; Patrix 0.0.0 i586)'; 
$rooturl     = 'https://patrick.net'; 
$user        = "pk"; 
$password    = "pw"; 
$gnuplot     = "/usr/local/bin/gnuplot";

# global objects:

$cookie_jar  = HTTP::Cookies->new; 
$ua          = LWP::UserAgent->new;

MAIN: { 
  $ua->agent($browser); # This sets browser for all uses of $ua.

  # home page 
  $latency = &get("/home.html"); 
  # verify that we got the page 
  $latency = -1 unless index "<title>login page</title>" > -1;
  &log("home.log", $latency); 
  sleep 2;

  $content = "user=$user&passwd=$password";

  # log in 
  $latency = &post("/login.cgi", $content); 
  $latency = -1 unless m|<title>welcome</title>|; 
  &log("login.log", $latency); 
  sleep 2;

  # content page 
  $latency = &get("/content.html"); 
  $latency = -1 unless m|<title>the goodies</title>|; 
  &log("content.log", $latency); 
  sleep 2;

  # logout 
  $latency = &get("/logout.cgi"); 
  $latency = -1 unless m|<title>bye</title>|; 
  &log("logout.log", $latency);

  # plot it all 
  `$gnuplot /home/httpd/public_html/demo.gp`; 
}

sub get { 
  local ($path) = @_;

  $request = new HTTP::Request('GET', "$rooturl$path");

  # If we have a previous response, put its cookies in the new request. 
  if ($response) { 
      $cookie_jar->extract_cookies($response); 
      $cookie_jar->add_cookie_header($request); 
  }

  if ($DEBUG) { 
      print $request->as_string(); 
  }

  # Do it. 
  $start    = time(); 
  $response = $ua->request($request); 
  $end      = time(); 
  $latency  = $end - $start;

  if (!$response->is_success) { 
      print $request->as_string(), " failed: ",
      $response->error_as_HTML; 
  }

  if ($DEBUG) { 
      print "\n## Got $path and result was:\n"; 
      print $response->content; 
      print   "## $path took $latency seconds.\n"; 
  }

  $latency; 
}

sub post {

  local ($path, $content) = @_;

  $header  = new HTTP::Headers; 
  $header->content_type('application/x-www-form-urlencoded'); 
  $header->content_length(length($content));

  $request = new HTTP::Request('POST', 
                               "$rooturl$path", 
                               $header, 
                               $content);

  # If we have a previous response, put its cookies in the new request. 
  if ($response) { 
      $cookie_jar->extract_cookies($response); 
      $cookie_jar->add_cookie_header($request); 
  }

  if ($DEBUG) { 
      print $request->as_string(); 
  }

  # Do it. 
  $start    = time(); 
  $response = $ua->request($request); 
  $end      = time(); 
  $latency  = $end - $start;

  if (!$response->is_success) { 
      print $request->as_string(), " failed: ", $response->error_as_HTML; 
  }

  if ($DEBUG) { 
      print "\n## Got $path and result was:\n"; 
      print $response->content; 
      print   "## $path took $latency seconds.\n"; 
  }

  $latency; 
}

# Write log entry in format that gnuplot can use to create an image. 
sub log {

  local ($file, $latency) = @_; 
  $date = `date +'%Y %m %d %H %M %S'`; 
  chop $date; 
  # Corresponding to gnuplot command: set timefmt "%m %d %H %M %S %y"

  open(FH, ">>$file") || die "Could not open $file\n";

  # Format printing so that we get only 4 decimal places. 
  printf FH "%s %2.4f\n", $date, $latency;

  close(FH); 
}

This gives a set of log files with timestamps and latency readings. To generate a graph from that, you need a gnuplot configuration file. Here's the gnuplot configuration file for plotting the home page times.

set term png color     
set output "/home/httpd/public_html/demo.png"     
set xdata time     
set ylabel "latency in seconds"     
set bmargin 3     
set logscale y     
set timefmt "%Y %m %d %H %M %S"     
plot "demo.log" using 1:7 title "time to retrieve home page"

Note that the output is set to write a PNG image directly into the web server's public_html directory. This way, you can merely click on a bookmark in your browser to see the output. Now just set up a cron job to run the monitor script every minute and you will have a log of the web page's performance and a constantly-updated graph. Use crontab -e to modify your crontab file. Here's an example entry in a crontab file.

# MIN   HOUR    DOM     MOY     DOW     Commands 
#(0-59) (0-23)  (1-31)  (1-12)  (0-6)   (Note: 0=Sun)
*       *        *       *       *      cd /home/httpd/public_html; ./monitor   

Figure 20-2. Graph of web site performance

Figure 20-3. Memory leaks

Figure 20-4. Database connection leaks

Figure 20-5. Database table indexed after May

Detailed instructions on how to set up your own monitoring and graphing system to make images like these can be found in Web Performance Tuning.

A final tip for system administrators: the recently introduced "selective acknowledgment" performance feature of TCP does not work with some old TCP stacks and older DSL hardware. Selective acknowledgment, or SACK, is defined in RFC 2018. The symptom is that browsers are occasionally sent blank pages and network error messages. Selective acknowledgment is supposed to work like this: say a server sends out four packets to a browser. Packet 2 gets lost while packets 1, 3, and 4 arrive just fine. Without selective acknowledgment, all a client can do is say that all packets arrived, or that they did not, and let the server time out and resend all 4 packets. But with selective acknowledgment, the client can tell the server exactly which packet was missing. This is a significant help to performance on lossy connections.

If you see some clients having network trouble upon upgrading your server to Solaris 8, this bug could be the cause. As of Solaris 8 the ndd parameter tcp_sack_permitted is 2. To fix the bug, you need only set it back to 1 or 0. The meanings of the 3 values of tcp_sack_permitted in Solaris's ndd command are:

0

Do not send or receive SACK information.

1

Do not initiate with SACK, but respond with SACK if other side does.

2

Initiate and accept connections with SACK.