ymmv
Update August 2015: If you are looking for locking and caching methods, lock_and_cache is a simpler alternative that is redis-only.
cache
Wraps memcached, redis, memcache-client, dalli and handles their weirdnesses, including forking.
Aims to let other libraries be cache-agnostic in return for a performance hit.
Real world usage
Used by lock_method and cache_method so that you can use them with memcached, redis, etc.
In production use at carbon.brighterplanet.com and data.brighterplanet.com.
Quick example
require 'memcached' # a really fast memcached client gem by Evan Weaver, one of the lead engineers at Twitter
require 'cache' # this gem, which wraps the client to provide a standard interface
client = Memcached.new('127.0.0.1:11211', :binary_protocol => true)
@cache = Cache.wrap(client)
# don't worry, even though it's memcached gem, this won't raise Memcached::NotFound
@cache.get('hello')
# fetch is not provided by the memcached gem, the wrapper adds it
@cache.fetch('hello') { 'world' }
# don't worry, the wrapper will automatically clone the Memcached object after forking (or threading for that matter)
Kernel.fork { @cache.get('hello') }
If you can't use the memcached gem (because you're on heroku, for example) then just wrap a dalli or a redis client. You still get exactly the same interface.
Rationale
I wanted a common interface to a bunch of great Ruby cache clients so I can develop gems (lock_method, cache_method) that accept any of them.
- I'm tired of rescuing from Memcached::NotFound
- I'm tired of forgetting whether it's :expires_in or :ttl
- I don't know why we ever started using read/write instead of get/set.
- I don't like how you have to manually handle after_fork for Redis, Memcached, etc.
- I don't know why Memcached::Rails doesn't act like a ActiveRecord::Cache::Store
- Why are you asking me about :raw or whatever? Just marshal it
Speed
It's more than 50% slower than raw Memcached and about the same as raw Dalli
# raw dalli versus wrapped
set: cache:dalli:bin 2.150000 0.840000 2.990000 ( 3.752008) <- Cache.wrap(Dalli::Client.new)
set: dalli:bin 2.120000 0.830000 2.950000 ( 3.734024) <- Dalli::Client.new
get: cache:dalli:bin 2.040000 0.910000 2.950000 ( 3.646148)
get: dalli:bin 2.040000 0.900000 2.940000 ( 3.632840)
delete: cache:dalli:bin 1.830000 0.880000 2.710000 ( 3.381917)
delete: dalli:bin 1.790000 0.880000 2.670000 ( 3.327514)
get-missing: cache:dalli:bin 1.780000 0.880000 2.660000 ( 3.344041)
get-missing: dalli:bin 1.760000 0.880000 2.640000 ( 3.337539)
set-large: cache:dalli:bin 2.750000 0.880000 3.630000 ( 4.474265)
set-large: dalli:bin 2.720000 0.870000 3.590000 ( 4.436163)
get-large: cache:dalli:bin 2.420000 0.990000 3.410000 ( 4.135326)
get-large: dalli:bin 2.410000 0.990000 3.400000 ( 4.119832)
# raw memcached versus wrapped
set: cache:libm:bin 0.860000 0.640000 1.500000 ( 3.033145) <- Cache.wrap(Memcached.new(:binary_protocol => true))
set: libm:bin 0.200000 0.480000 0.680000 ( 1.907099) <- Memcached.new(:binary_protocol => true)
get: cache:libm:bin 0.800000 0.680000 1.480000 ( 2.700458)
get: libm:bin 0.260000 0.660000 0.920000 ( 1.974025)
delete: cache:libm:bin 1.000000 0.600000 1.600000 ( 2.968057)
delete: libm:bin 0.600000 0.560000 1.160000 ( 2.375070)
get-missing: cache:libm:bin 0.980000 0.800000 1.780000 ( 2.850947)
get-missing: libm:bin 0.640000 0.710000 1.350000 ( 2.520733)
set-large: cache:libm:bin 1.220000 0.590000 1.810000 ( 3.404739)
set-large: libm:bin 0.230000 0.520000 0.750000 ( 2.111738)
get-large: cache:libm:bin 3.780000 0.870000 4.650000 ( 6.073208)
get-large: libm:bin 0.340000 0.830000 1.170000 ( 2.304408)
Thanks to https://github.com/evan/memcached/blob/master/test/profile/benchmark.rb
So: hopefully it makes it easier to get started with caching and hit the low-hanging fruit. Then you can move on to a raw client!
Features
Forking/threading
When you use a Cache object to wrap Memcached or Redis, you don't have to worry about forking or threading.
For example, you don't have to set up unicorn or PhusionPassenger's after_fork.
TTL
0 means don't expire.
The default ttl is 60 seconds.
Marshalling
Everything gets marshalled. No option to turn it into "raw" mode. If you need that kind of control, please submit a patch or just use one of the other gems directly.
Methods
It will translate these methods to whatever Redis, Memcached, etc. client you're using:
@cache.get 'hello'
@cache.set 'hello', 'world', 5.minutes
@cache.delete 'hello'
@cache.flush
@cache.exist? 'hello'
@cache.reset
@cache.fetch 'hello' { 'world' }
@cache.cas 'hello' { |current| 'world' }
@cache.increment 'high-fives'
@cache.decrement 'high-fives'
@cache.get_multi 'hello', 'privyet', 'hallo'
Also provided for Rails compatibility:
@cache.write 'hello', 'world', :expires_in => 5.minutes
@cache.read 'hello'
@cache.clear
@cache.compare_and_swap
@cache.read_multi 'hello', 'privyet', 'hallo'
Supported clients
Supported memcached clients:
- memcached (native C extensions, super fast!)
- dalli (pure ruby, recommended if you're on heroku)
- memcache-client (not recommended. the one that comes with Rails.)
Supported Redis clients:
How you might use it
| Super-fast memcached | Pure Ruby memcached (works on Heroku) | Redis | |
|---|---|---|---|
| Rails | config.cache_store = Cache.wrap(Memcached.new) |
config.cache_store = Cache.wrap(Dalli::Client.new) |
config.cache_store = Cache.wrap(Redis.new) |
| Your own library |
# Accept any client, let Cache take care of it def cache=(raw_client) @cache = Cache.wrap(raw_client) end |
# Accept any client, let Cache take care of it def cache=(raw_client) @cache = Cache.wrap(raw_client) end |
# Accept any client, let Cache take care of it def cache=(raw_client) @cache = Cache.wrap(raw_client) end |
| CacheMethod (already uses Cache internally) | CacheMethod.config.storage = Memcached.new |
CacheMethod.config.storage = Dalli::Client.new |
CacheMethod.config.storage = Redis.new |
| LockMethod (already uses Cache internally) | LockMethod.config.storage = Memcached.new |
LockMethod.config.storage = Dalli::Client.new |
LockMethod.config.storage = Redis.new |
Other examples
It defaults to an in-process memory store:
@cache = Cache.new
@cache.set 'hello', 'world'
@cache.get 'hello'
You can specify a more useful cache client:
require 'redis' # the redis key-value store
require 'cache' # this gem, which provides a standard interface
raw_client = Redis.new
@cache = Cache.wrap(raw_client)
or
require 'dalli' # the dalli memcached client used by heroku
require 'cache' # this gem, which provides a standard interface
raw_client = Dalli::Client.new
@cache = Cache.wrap(raw_client)
Or you could piggyback off the default rails cache:
@cache = Cache.wrap(Rails.cache)
Copyright
Copyright 2011 Seamus Abshere