I was running W3 Total Cache on four blogs using APC & MaxCDN with great success. I was running on LiquidWeb VPS, and I recently upgraded to StormOnDemand to a machine with 5x the memory and cpu resources. Now I am having nothing but problems with APC cache enabled. PHP memory exhausted errors and unable to allocate memory for pool keep popping up constantly. Restart Apache and they start up again shortly after. These started immediately after enabling APC cache, but ran this for almost a year without problems with a VPS with only 384MB now it is running on 1.8GB of ram.
I enabled XCache temporarily, but I can't seem to figure out why it was working fine for a year before and a new server with a lot more resources and having nothing but problems.
I updated PHP memory to 64MB yet it still was throwing errors. When I was running APC, I updated the APC memory setting to 64MB as well. There is almost no traffic on this site at the time of these problems, it was just me logging into WordPress editing pages, few minutes later it bombs.