By means of CGI::Carp I have been able to force the error to reveal itself to me at last.

The error is a familiar one, and expected:

Had to create DBD::mysql::dr::imp_data_size unexpectedly at /usr/lib/perl5/DBI.pm line 1190.

Now, it might be worthwhile or interesting for you to know, at least for the record, how I managed to get this far. Here's the magick:

BEGIN {
  $ENV{'LD_LIBRARY_PATH'} = '/lib/tls';

  use FindBin qw($Bin);
  use lib ("$Bin/../../lib",
           "$Bin/../../../local-perl/lib/perl/5.8.8",
           "$Bin/../../../local-perl/share/perl/5.8.8",
           '/var/www/perl5/lib/perl5/site_perl/5.8.8',
           '/var/www/perl5/lib/perl5/5.8.8/i686-linux',
           '/var/www/perl5/lib/perl5'
          );

# RELEVANT STUFF STARTS HERE:
  my $path="$Bin/../../log/carpout.log";
no strict 'refs';
no strict 'subs';
  open(LOG, ">>$path") or
    die("Unable to open mycgi-log: $!\n");
  carpout(LOG);
}
[download]

To review... The first part of the block is simply my program's way of establishing connection to the local-copy CPAN library modules that it uses. FindBin is the ever-helpful standard module that will tell you where the program that you are running is actually located. The use lib directives then place relative pathnames based on this at the front of the @INC list.

The magick starts after the comment:   # RELEVANT STUFF STARTS HERE.

In my ongoing pursuit of this problem, I have also found the CPAN module on “troubleshooting mod_perl problems,” (simply titled troubleshooting ...) to be particularly informative. I have not yet completely solved my problem, but I'm well on my way.