Checking APC while optimizing my cache routine for Pretty Urls, I noticed I am getting allot of extra caches due to filemtime in the key generation in Load.php.
I am unsure what to make of it but it looks like the file times aren't the same on each of the servers in the grid and this is causing different keys for the same cache depending on which server is processing the script at the time.
In the past I thought this was being caused by each server having their own APC memory but it looks like this memory is synced between the grid and the caches inconsistencies that I have experienced are easily fixable by changing the way the keys are generated.