1. CHI: Universal caching
for Perl
Jonathan Swartz
YAPC::NA 2012
Madison, WI

2. What is CHI?
• Cache Handling Interface
• Standard interface and implementation for Perl
caching ... like 'DBI for caching'
• Caching = “Get and set key/values with expiration”

3. We already have...

4. What’s it good for?
• Implement standard caching features in a single place
• Namespaces • Logging
• Serialization • Statistics collection
• Multilevel caches • Error handling
• Probablistic expiration • Compression
• Max size and discard • Configuration
• Make new cache backends trivial to create

5. Who needs caches?
• Web frameworks (Catalyst, Dancer, ...)
• Sessions (Plack::Session, CGI::Session, ...)
• ORMs (DBIx::Class, RDBO, ...)
• Templating (TT, Mason, ...)
• Code processing (Perl::Tidy, Perl::Critic, ...)
• Slow to startup (Class::MOP/Moose, ...)

6. Using CHI

7. Namespaces
• Separate cache keys into silos
• Can be inspected, configured, and cleared
independently
• Typically package or template name

8. Drivers
• Memory/RawMemory - In-process memory
• File - Hierarchical, one file per entry
• FastMmap - Mmap'ed files
• BerkeleyDB
• DBI
• Memcached, Redis, TokyoTyrant - Distributed
• ...

9. Probabilistic expiration
• Good for avoiding “miss stampedes”

10. L1/L2 cache
• Store sessions in mysql, fronted by memcached

11. Mirror cache
• Migrate cache from /old/root to /new/root

12. CHI::Memoize
• Like Memoize, only CHI-ier

13. Why is compute() better?
• Less typing
• Background recomputation *
(return old value immediately, recompute in background)
• Can measure compute time and thus cache utility
* - theoretical, not yet implemented

14. Cache utility
HR = hit rate
Cget = cost of get
Cset = cost of set
Ccompute = cost of compute
Cget + (Ccompute + Cset) / HR
Utility = -------------------------------
Ccompute

15. Stats

16. Stats collected per namespace
• # hits, misses, and sets hit rate
• avg cost of get, set, and compute (ms)
• avg key and value size

17. Resources
• Get CHI from CPAN -
http://search.cpan.org/perldoc?CHI
• Search for drivers -
http://cpan.uwinnipeg.ca/search?query=CHI::Driver
• Subscribe to perl-cache mailing list -
http://groups.google.com/group/perl-cache-discuss

19. Benchmarks
Description Get time Set time
CHI::Driver::MemoryRaw 0.019ms 0.036ms
CHI::Driver::Memory 0.042ms 0.066ms
CHI::Driver::BerkeleyDB 0.052ms 0.073ms
CHI::Driver::FastMmap 0.057ms 0.087ms
CHI::Driver::DBI (sqlite) 0.112ms 1.659ms
CHI::Driver::File 0.118ms 1.138ms
CHI::Driver::Memcached::Fast 0.138ms 0.178ms
CHI::Driver::Memcached::libm 0.151ms 0.202ms
CHI::Driver::DBI (mysql) 0.236ms 0.273ms
CHI::Driver::Memcached 0.279ms 0.235ms

20. Creating a driver

21. Creating a cache
my $cache = CHI->new(
driver => 'File',
namespace => ‘Foo::Bar’,
cache_root => '/path/to/root'
);
my $cache = CHI->new(
driver => 'FastMmap',
root_dir => '/path/to/root',
cache_size => '1k'
);
my $cache = CHI->new(
driver => 'Memcached',
servers => ["10.0.0.15:11211”, ...]
);