we are using mysql 4.1.xx

i discovered our problem was the default mysql table format (MyISAM) locks the entire table when querying.. so we´ll change to InnoDB table type, that locks just the register... avoinding a query queue on the server... i suposed (and hope) this gonna work..

i wonder if there is nothing similar on postgress that could be the cause of your problem

memory and process parameters are also important (max clients and max connections, for apache and your database)

there is a formula that defines max_clients somewhere on this forum...

and more important: there is a moodle/admin/dbperformance.php file that can helps a lot...

cheers