Tuning APC

Configuration

• Old opcodes stay in cache until all old requests satisfied. Leave headroom (up to 2x normal size).
• Add hints
• Set apc.stat = 0
  • But have to restart server to get new files
• With source control, use apc.stat_ctime = 1 if apc.stat = 1.

• Compile using spin locks. Use pthreads if spins fail.

Ideas

• Try experimental functions apc_bindump_file() and apc_binload_file().
• On deployment, serialize the cache and load in the serialized cache to every server while under maintenance.
• Use apc_compile_file() to prime/update the cache.
• User variable cache: apc_fetch(), but must serialize to use memcached.
• Check if latest APC uses double-linked lists for less performance trouble with fragmentation.
• Check out lazy loading (a PHP 5.3 patch).
• Use APCIterator().
• Check out APC 4.0 with LFU support, which supports multiple caches.

Other notes

• No sharing of compiled code between FastCGI threads
• Significant copying of compiled code between Apache/mod_php threads