I am using the SuSE 9.1 which has apache 2.0 and mod_perl 1.99_12.
I did not see any Apache::DBI debug information in the apache error log.
jiesheng, please read the module's manpage: http://search.cpan.org/dist/Apache-DBI/DBI.pm
To enable debugging the variable $Apache::DBI::DEBUG must be set. This can either be done in startup.pl or in the user script. Setting the variable to 1, just reports about a new connect. Setting the variable to 2 enables full debug output.
I indeed set the $Apache::DBI::DEBUG=2 in the /etc/apache2/mod_perl-startup.pl. However I did not see any debug output in the apache error log file
