LruRedux

An efficient, thread safe LRU cache.

• Installation
• Usage
  • TTL Cache
• Cache Methods
• Benchmarks
• Other Caches
• Contributing
• Changelog

Installation

Add this line to your application’s Gemfile:

gem 'lru_redux'

And then execute:

$ bundle

Or install it yourself as:

$ gem install lru_redux

Ruby 1.8 - v0.8.4 is the last compatible release:

gem 'lru_redux', '~> 0.8.4'

Usage

require 'lru_redux'

# non thread safe
cache = LruRedux::Cache.new(100)
cache[:a] = "1"
cache[:b] = "2"

cache.to_a
# [[:b,"2"],[:a,"1"]]
# note the order matters here, last accessed is first

cache[:a] # a pushed to front
# "1"

cache.to_a
# [[:a,"1"],[:b,"2"]]
cache.delete(:a)
cache.each {|k,v| p "#{k} #{v}"}
# b 2

cache.max_size = 200 # cache now stores 200 items
cache.clear # cache has no items

cache.getset(:a){1}
cache.to_a
#[[:a,1]]

# already set so don't call block
cache.getset(:a){99}
cache.to_a
#[[:a,1]]

# for thread safe access, all methods on cache
# are protected with a mutex
cache = LruRedux::ThreadSafeCache.new(100)

TTL Cache

The TTL cache extends the functionality of the LRU cache with a Time To Live eviction strategy. TTL eviction occurs on every access and takes precedence over LRU eviction, meaning a ‘live’ value will never be evicted over an expired one.

# Timecop is gem that allows us to change Time.now
# and is used for demonstration purposes.
require 'lru_redux'
require 'timecop'

# Create a TTL cache with a size of 100 and TTL of 5 minutes.
# The first argument is the size and
# the second optional argument is the TTL in seconds.
cache = LruRedux::TTL::Cache.new(100, 5 * 60)

Timecop.freeze(Time.now)

cache[:a] = "1"
cache[:b] = "2"

cache.to_a
# => [[:b,"2"],[:a,"1"]]

# Now we advance time 5 min 30 sec into the future.
Timecop.freeze(Time.now + 330)

# And we see that the expired values have been evicted.
cache.to_a
# => []

# The TTL can be updated on a live cache using #ttl=.
# Currently cached items will be evicted under the new TTL.
cache[:a] = "1"
cache[:b] = "2"

Timecop.freeze(Time.now + 330)

cache.ttl = 10 * 60

# Since ttl eviction is triggered by access,
# the items are still cached when the ttl is changed and
# are now under the 10 minute TTL.
cache.to_a
# => [[:b,"2"],[:a,"1"]]

# TTL eviction can be triggered manually with the #expire method.
Timecop.freeze(Time.now + 330)

cache.expire
cache.to_a
# => []

Timecop.return

# The behavior of a TTL cache with the TTL set to `:none`
# is identical to the LRU cache.

cache = LruRedux::TTL::Cache.new(100, :none)

# The TTL argument is optional and defaults to `:none`.
cache = LruRedux::TTL::Cache.new(100)

# A thread safe version is available.
cache = LruRedux::TTL::ThreadSafeCache.new(100, 5 * 60)

Cache Methods

• #getset Takes a key and block. Will return a value if cached, otherwise will execute the block and cache the resulting value.
• #fetch Takes a key and optional block. Will return a value if cached, otherwise will execute the block and return the resulting value or return nil if no block is provided.
• #[] Takes a key. Will return a value if cached, otherwise nil.
• #[]= Takes a key and value. Will cache the value under the key.
• #delete Takes a key. Will return the deleted value, otherwise nil.
• #evict Alias for #delete.
• #clear Clears the cache. Returns nil.
• #each Takes a block. Executes the block on each key-value pair in LRU order (most recent first).
• #to_a Return an array of key-value pairs (arrays) in LRU order (most recent first).
• #key? Takes a key. Returns true if the key is cached, otherwise false.
• #has_key? Alias for #key?.
• #count Return the current number of items stored in the cache.
• #max_size Returns the current maximum size of the cache.
• #max_size= Takes a positive number. Changes the current max_size and triggers a resize. Also triggers TTL eviction on the TTL cache.

TTL Cache Specific

• #ttl Returns the current TTL of the cache.
• #ttl= Takes :none or a positive number. Changes the current ttl and triggers a TTL eviction.
• #expire Triggers a TTL eviction.

Benchmarks

see: benchmark directory (a million random lookup / store)

LRU

Ruby 2.2.1

$ ruby ./bench/bench.rb

Rehearsal -------------------------------------------------------------
ThreadSafeLru               4.500000   0.030000   4.530000 (  4.524213)
LRU                         2.250000   0.000000   2.250000 (  2.249670)
LRUCache                    1.720000   0.010000   1.730000 (  1.728243)
LruRedux::Cache             0.960000   0.000000   0.960000 (  0.961292)
LruRedux::ThreadSafeCache   2.180000   0.000000   2.180000 (  2.187714)
--------------------------------------------------- total: 11.650000sec

                                user     system      total        real
ThreadSafeLru               4.390000   0.020000   4.410000 (  4.415703)
LRU                         2.140000   0.010000   2.150000 (  2.149626)
LRUCache                    1.680000   0.010000   1.690000 (  1.688564)
LruRedux::Cache             0.910000   0.000000   0.910000 (  0.913108)
LruRedux::ThreadSafeCache   2.200000   0.010000   2.210000 (  2.212108)

Ruby 2.0.0-p643

Implementation is slightly different for Ruby versions before 2.1 due to a Ruby bug. http://bugs.ruby-lang.org/issues/8312

$ ruby ./bench/bench.rb
Rehearsal -------------------------------------------------------------
ThreadSafeLru               4.790000   0.040000   4.830000 (  4.828370)
LRU                         2.170000   0.010000   2.180000 (  2.180630)
LRUCache                    1.810000   0.000000   1.810000 (  1.814737)
LruRedux::Cache             1.330000   0.010000   1.340000 (  1.325554)
LruRedux::ThreadSafeCache   2.770000   0.000000   2.770000 (  2.777754)
--------------------------------------------------- total: 12.930000sec

                                user     system      total        real
ThreadSafeLru               4.710000   0.060000   4.770000 (  4.773233)
LRU                         2.120000   0.010000   2.130000 (  2.135111)
LRUCache                    1.780000   0.000000   1.780000 (  1.781392)
LruRedux::Cache             1.190000   0.010000   1.200000 (  1.201908)
LruRedux::ThreadSafeCache   2.650000   0.010000   2.660000 (  2.652580)

TTL

Ruby 2.2.1

$ ruby ./bench/bench_ttl.rb
Rehearsal -----------------------------------------------------------------------
FastCache                             6.240000   0.070000   6.310000 (  6.302569)
LruRedux::TTL::Cache                  4.700000   0.010000   4.710000 (  4.712858)
LruRedux::TTL::ThreadSafeCache        6.300000   0.010000   6.310000 (  6.319032)
LruRedux::TTL::Cache (TTL disabled)   2.460000   0.010000   2.470000 (  2.470629)
------------------------------------------------------------- total: 19.800000sec

                                          user     system      total        real
FastCache                             6.470000   0.070000   6.540000 (  6.536193)
LruRedux::TTL::Cache                  4.640000   0.010000   4.650000 (  4.661793)
LruRedux::TTL::ThreadSafeCache        6.310000   0.020000   6.330000 (  6.328840)
LruRedux::TTL::Cache (TTL disabled)   2.440000   0.000000   2.440000 (  2.446269)

Other Caches

This is a list of the caches that are used in the benchmarks.

LRU

• RubyGems: https://rubygems.org/gems/lru
• Homepage: http://lru.rubyforge.org/

LRUCache

• RubyGems: https://rubygems.org/gems/lru_cache
• Homepage: https://github.com/brendan/lru_cache

ThreadSafeLru

• RubyGems: https://rubygems.org/gems/threadsafe-lru
• Homepage: https://github.com/draganm/threadsafe-lru

FastCache

• RubyGems: https://rubygems.org/gems/fast_cache
• Homepage: https://github.com/swoop-inc/fast_cache

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Changelog

version 1.1.0 - 30-Mar-2015

• New: TTL cache added. This cache is LRU like with the addition of time-based eviction. Check the Usage -> TTL Cache section in README.md for details.

version 1.0.0 - 26-Mar-2015

• Ruby Support: Ruby 1.9+ is now required by LruRedux. If you need to use LruRedux in Ruby 1.8, please specify gem version 0.8.4 in your Gemfile. v0.8.4 is the last 1.8 compatible release and included a number of fixes and performance improvements for the Ruby 1.8 implementation. @Seberius
• Perf: improve performance in Ruby 2.1+ on the MRI @Seberius

version 0.8.4 - 20-Feb-2015

• Fix: regression of ThreadSafeCache under JRuby 1.7 @Seberius

version 0.8.3 - 20-Feb-2015

• Perf: improve ThreadSafeCache performance @Seberius

version 0.8.2 - 16-Feb-2015

• Perf: use #size instead of #count when checking length @Seberius
• Fix: Cache could grow beyond its size in Ruby 1.8 @Seberius
• Fix: #each could deadlock in Ruby 1.8 @Seberius

version 0.8.1 - 7-Sep-2013

• Fix #each implementation
• Fix deadlocks with ThreadSafeCache
• Version jump is because its been used in production for quite a while now

version 0.0.6 - 24-April-2013

• Fix bug in getset, overflow was not returning the yeilded val

version 0.0.5 - 23-April-2013

• Added getset and fetch
• Optimised implementation so it 20-30% faster on Ruby 1.9+

version 0.0.4 - 23-April-2013

• Initial version