I'm doing a custom page that has multiple wp query calls, the thing is that I don't need the main query that is I don't need anything from the page contents, so in order to save load time I was wondering how to tell wordpress not to fetch anything from the db ?
I would highly recommend you to make one of those wp query calls the main query & all others as secondary queries. That will make your life much easier in the long run.
If you absolutely want to disable the main query, wordpress doesn't have a direct filter for that. You can however do a trick to achieve that
This should work, however you should note that, since wordpress never got a chance to populate the global variables, accessing them directly or via some core wordpress function will have unexpected results. Next, some plugins may also have problems. Make sure you carefully test all of the code you're using.