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Caching for Cash: Caching

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Caching for Cash: Caching

  1. 1. CACHING FOR CASH - CACHING Scott MacVicar php|works 2008
  2. 2. WHY CACHE? Reduce memory usage Reduce processing time Reduce network traffic Reduce disk access
  3. 3. CACHING OPTIONS Flat file RAM disk Database Memcache APC Script level
  4. 4. WHAT TO CACHE? External resources Large result sets Static data Sessions
  5. 5. FLAT FILE CACHE Write data out to a local file Config files from Database or XML Remote resources store locally Output buffering to local file
  6. 6. CACHING FILES PEAR::Cache_Lite Zend_Cache in Zend Framework var_export in PHP
  7. 7. RAM DISK Mount some memory as disk space Used when IO actions can’t be avoided Non resizable on the fly
  8. 8. LIGHTTPD + PHP Lua is a scripting language in lighttpd Use PHP to write out file to disk Have Lua look at the modified time of the file, if within the limit serve else execute PHP
  9. 9. MEMCACHE Origins within Livejournal Used by Facebook, Youtube, Wikipedia and digg Caching daemon, no persistence Stores key / value pairs
  10. 10. FACEBOOK EXAMPLE 200 dedicated memcache servers Each 16GB quad-core amd64 3TB memcache data
  11. 11. MEMCACHE Slab Allocator Libevent based (non-blocking) Simple Protocol Server is just a hash table No authentication or self awareness
  12. 12. MEMCACHE CLIENT Clients provide key and value Responsible for serialising any value Compress data
  13. 13. SERVER PROTOCOL set/replace/add get append/prepend increment/decrement compare and swap
  14. 14. HASHING Key is hashed into a value Modulous then applied which is the number of the servers Server is then picked and stored If one server drops out you only lose a fraction of the keys
  15. 15. MEMCACHE LIMITS Key Size is 250 bytes Data Size is 1 megabyte 32bit/64bit memory limit No Replication across cluster
  16. 16. MEMCACHE CLEANING UP Uses Least Recently Used Algorithm Looks for the oldest item and removes TTL also applies to key / value pairs
  17. 17. SIMPLE USAGE Fetch from memcache If there return Else calculate, store in cache and return
  18. 18. WHERE TO RUN? Any server works No need for matching size Low CPU usage
  19. 19. MEMCACHE + PHP PECL extension using custom connection pecl install memcache Provides MemcachePool and Memcache INI settings to change hash strategy, function and protocol.
  21. 21. MEMCACHE ACTIONS Add - only if the key doesn’t exist Set - will add or update key Replace - only if the key already exists
  22. 22. MEMCACHE TASK Open Terminal in VMWare Image and run sudo service memcached start Try using memcache to set, get and add values Try setting a value using the Time To Live parameter Ask questions :-)
  23. 23. MEMCACHEDB Persistent key/value storage system BDB used for persitence Compatible with Memcache protocol
  24. 24. MEMCACHEDB CAVEATS No expiration Isn’t a replacement for memcache
  25. 25. APC Provides OPCode caching in PHP Shared memory for storage APC is only on the local server No network overhead from TCP/IP
  26. 26. APC Input Tokenizer Parser APC Compiler Store Opcodes Executor
  27. 27. APC SAMPLE
  28. 28. CACHE LAYERING Disk / APC Memcache Database Fetch from APC locally Fetch from Memcache, add to APC Finally fetch from the original source and store back in Memcache
  29. 29. APC USE CASES Should always use it to cache opcode of files Small but frequently accessed things You only have one server
  30. 30. APC TASK Try storing classes or arrays in APC Use the Time To Live APC supports an array for keys in apc_get, fetch multiple values
  31. 31. SQLITE Local node storage of filesystem Cache result sets from remote database In memory database
  32. 32. DATABASE QUERY CACHING Rely on MySQL to do the query caching Doesn’t quite work though :-( Invalidation of cache happens easily
  33. 33. ALTERNATIVE DATABASE CACHING Store the result set from the database using another caching software Hash query as a key value Extend your DB layer to add this transparently?
  34. 34. CACHING TIPS Pre-heat the cache Use multiple levels of cache Cache even dynamic data for short times serialize() is slow
  35. 35. QUESTIONS?