1. Caching: A Guided Tour
Jason Ragsdale - DPUG 10/12/2010

2. Overview
• When to cache?
• What to cache?
• Page, Fragment and Data
• File system, Database and In-Memory
• Managing your TTL’s
• Clearing / Invalidation

3. When to cache?
• When you are accessing:
• Read only / mostly static data
• High latency external services
• Repeated page segments

4. When to cache?
• Short answer : Always

5. What to cache?
• Database data
• Web service data
• Dynamically generated content

6. Page caching
• Caching the content of a whole page

7. Fragment caching
• Caching a portion of a page

8. Data caching
• Storing of return data from a service
• Database
• Web services

9. File system
• PRO:
• Fast (depending on hardware)
• Persistent data
• Can operate on data via cron jobs

10. File system
• CON:
• Slow (depending on hardware)
• Open file limits of OS
• Max inode limits of OS/FS
• File lock issues on writes
• Does not scale well

11. Database
• PRO:
• Fast - Can rely on DB caching
• Flexable - Can scale
• Persistent data
• Can operate on data via cron jobs

12. Database
• CON:
• Relying on the DB being available
• Caching DB data back into the DB
• Flat file DB’s can have file lock issues

13. Database - Clarification
• When speaking of DB caching we are
talking about caching of content into a table
not the caching mechanisms of the DB
itself.

14. In-Memory
• PRO:
• Fast: Local memory access is cheap
• Distributed access is cheap (network)
• Flexible - can scale

15. In-Memory
• CON:
• Non-Persistent data (normally)
• No security built in

16. Managing your TTL’s
• Same content called from multiple API’s
• API 1 want’s data that is no older than 1
hour
• API 2 want’s data that is no older than 24
hours

17. Clearing your cache
• Data is no longer valid
• Clear to force a new call to the fresh data

18. Invalidating your cache
• What if you do not know all possible keys?
• Item ‘123456’
• ‘123456_methodname_param’
• You do not know all ‘methodnames’ or
‘params’

19. Invalidating your cache
• Create a “key” that you can invalidate
• Create a cache entry ‘ver_123456’ with
the value of the current unixtime
• ‘123456_unixtime_methodname_param’
• Now you can invalidate an item just by
changing the value of the ‘ver’ record, TTL
will take care old ver’s

20. <?php time
• pecl/apc
• pecl/memcache
• pecl/memcached (huh? two of them?)

21. APC
• Built in cache for php (may have to compile
it)
• Provides opcode caching
• Provides ability to cache data

22. APC (the dark side)
• Cache race/locking/overwriting issues

23. memcached
• Fast
• Easy to set up
• Easy to configure for distributed caching

24. cache_object
• __call - Where the magic happens

25. Q&A