[horde] horde logging with mysql problem ?

[alex]

Hi all:
runtime env:apache+php4+imp4
I used mysql as logging stroage,and here are some of config item in 
horde/config/conf.php
$conf['log']['type'] = 'sql';
$conf['log']['name'] = 'log_table';
$conf['log']['params'] = array();
$conf['log']['params']['phptype'] = 'mysql';
$conf['log']['params']['hostspec'] = 'mysql.my.com';
$conf['log']['params']['username'] = 'root';
$conf['log']['params']['password'] = '***';
$conf['log']['params']['database'] = 'horde';

even drop all uniq indexes in log_table,but still occur such errors:

Notice: Undefined index: dsn in /usr/local/lib/php/Log/sql.php on line 55
Fatal error: Call to undefined function: query()
in /usr/local/lib/php/Log/sql.php on line 114

Alex
P.S: runtime env:apache+php4+imp4+mysql