Select mysql but install_driver(Pg) failed

i reinstalled RT in default setup (with mysql) but when acceding index
through browser, i get the following in httpd error_log

[Sat Mar 17 16:11:49 2007] [error] install_driver(Pg) failed: Can’t
locate DBD/ in @INC (@INC contains: /var/www/rt3/local/lib
/usr/local/libdata/perl5/i386-openbsd/5.8.8 /usr/libdata/perl5
/usr/local/libdata/perl5 /usr/local/libdata/perl5/site_perl/i386-openbsd
perl/i386-openbsd /usr/local/libdata/perl5/site_perl
/usr/libdata/perl5/site_perl /usr/local/lib/perl5/site_perl . /var/www/
/var/www/lib/perl) at (eval 261) line 3.\nPerhaps the DBD::Pg perl module h
asn’t been fully installed,\nor perhaps the capitalisation of ‘Pg’ isn’t
right.\nAvailable drivers: DBM, ExampleP, File, Gofer, Proxy, SQLite,
Sponge, mysql.\n at /var/www/usr/perl5rt/libdata/perl5/si
te_perl/DBIx/SearchBuilder/ line 106\n

in the Makefile of src when building, there is mysql. why i have Pg now ?
a way to check mysql is really selected ?

setup is
RT 3.6.3
OpenBSD 4.0-stable/i386, Apache 1, mod_perl 1.29