WordPress multisite memory allocation question.

I’m learning about WordPress memory allocation, which oddly seems to be quite important for WordPress functioning correctly but isn’t even mentioned on their systems requirements page. From what I’ve found so far WordPress needs 32MB min and WordPress Multisite needs 64MB min.

Whatever amount you allocate to WordPress you also have to make sure that PHP has at least that same amount allocated to it. But I’ve got some questions because I’ve talked to tech support at two different hosts now and they are saying things that just don’t seem right to me. I’d like to get some clarification if anyone knows the answers.

Rackspace tech support said that they have lots of WordPress Multisites running on their servers and he was adamant that they all run just fine on no more than 40MB. Yet WordPress says 64MB and the site I’ve currently got in development (no traffic yet) is using about 45MB just with Catalyst, Gravity and about 15 other plugins, most of them with small memory footprints. Does anyone have experience with WP Multisites and how much memory they actually need once they have multiple sites and traffic?

The MediaTemple tech support said that if I allocate 64MB to PHP, and there are 5 pages being loaded (page requests) it’s going to use 320MB of memory! That doesn’t even make sense to me unless each of those pages is very inefficient, I can’t believe the amount you allocate is what PHP uses for each page request no matter what is required. If anyone can clarify this for me I’d be grateful. So when you allocate memory to PHP (eg 64MB) are you telling it, use this much (64MB) for each request, or are you saying, collectively all the page requests you can handle at any one time have to use this much (64MB) or less? If it’s the latter, this will sound like a really stupid question, but I’m only asking because this tech guy made it sound like the former is what happens. So I just want to make sure.

Do all the WordPress operations try to execute in that 64MB that’s been allocated to it? Or is every page request going to be using that much like the tech support suggested would happen for separate PHP scripts.