Here was my setup on an Amazon Medium Instance using APC: php.ini configuration [APC] extension=apc.so apc.enabled=1 apc.shm_segments=1 ;32M per WordPress install apc.shm_size=128M ;Relative to the number of cached files (you may need to watch your stats for a day or two to find out a good number) apc.num_files_hint=7000 ;Relative to the size of WordPress apc.user_entries_hint=4096 ;The number of