Exactly why I can not make use of the normal 404.php Wordpress template file is due to my host. An IP (crawler maybe) stored viewing 404 pages and delivering SQL queries I suppose. Since I am on the shared host, they explained to set up Wordpress Super Cache (that we did) and add an ErrorDocument 404 directive during my htaccess file but that does not work.

Where it ought to be added therefore it overrides Wordpress default one?

Meanwhile, I have transformed the 404.php to some simple html file. That will not send any SQL demands right?

Thanks, Cris

The 404 page (such as the default one from Wordpress) should not be firing SQL queries. It is the page you finish on once the SQL has determined it cannot find what's being requested.

One common reason behind high SQL activity is when you've defined your permalink structure. It's tempting (but deadly) to make use of "postname". It's the most typical way I'm able to think about to stroll into this type of an issue.

But I am sure you will find more I've not discovered yet...