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Tuning APC

Tuning APC

Sept 24, 2009

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