to whom it may concern on this ticket.
i have had this problem on plesk for windows server for a long time. it is very frustrating. there are no easy or miracle answers, either.
.ini files, .cnf files., php. ini files. there are just no easy answers. we've tried them all. done a ton of reading and found posts and things on the internet saying what the problem is, and the fix... and, they aint.
SW tries to help but as of yet no cures. in fact once you get their attention, SW always tries to help out regardless of issue, so in this regard i cannot knock them. i sure wish there was an answer to this problem, however.
if anyone has that magical cure, you be sure to let me know....
my thought is if you think you have the cure, you probably don't. we upgrade version of 4.x and that didnt help either.
personally i never experienced this kind of problem on servers not running vz or plesk. however that isnt to say that servers without vz or plesk don't exhibit the problem, either. just my owen experience with mysql on wink2 and win2k3 servers.
those having the problem you are warned. there is no easy answer except maybe start offloading php/mysql sites to a more lightly loaded node whether you think you should have to or not.
hope it helps.
p.s. somewhere in this thread aw stats calc. was intertwined. i'll attest these servers have troubles completing aw calc, for sure, when domains start adding up on a server. we have more than one plesk in windows server to observe the same problems over time. it takes a long time to calc, and eventually won't complete as time goes on. we turned them off to save the serever the resource and offer something else now upon request. again, never had this problem prior to vz/plesk server with AW, however we dont like AW or webalizer anyway, so no great loss.