class ActiveSupport::Cache::Store

An abstract cache store class. There are multiple cache store implementations, each having its own additional features. See the classes under the ActiveSupport::Cache module, e.g. ActiveSupport::Cache::MemCacheStore. MemCacheStore is currently the most popular cache store for large production websites.

Some implementations may not support all methods beyond the basic cache methods of fetch, write, read, exist?, and delete.

ActiveSupport::Cache::Store can store any serializable Ruby object.

cache = ActiveSupport::Cache::MemoryStore.new

cache.read('city')   # => nil
cache.write('city', "Duckburgh")
cache.read('city')   # => "Duckburgh"

Keys are always translated into Strings and are case sensitive. When an object is specified as a key and has a cache_key method defined, this method will be called to define the key. Otherwise, the to_param method will be called. Hashes and Arrays can also be used as keys. The elements will be delimited by slashes, and the elements within a Hash will be sorted by key so they are consistent.

cache.read('city') == cache.read(:city)   # => true

Nil values can be cached.

If your cache is on a shared infrastructure, you can define a namespace for your cache entries. If a namespace is defined, it will be prefixed on to every key. The namespace can be either a static value or a Proc. If it is a Proc, it will be invoked when each key is evaluated so that you can use application logic to invalidate keys.

cache.namespace = -> { @last_mod_time }  # Set the namespace to a variable
@last_mod_time = Time.now  # Invalidate the entire cache by changing namespace

Cached data larger than 1kB are compressed by default. To turn off compression, pass compress: false to the initializer or to individual fetch or write method calls. The 1kB compression threshold is configurable with the :compress_threshold option, specified in bytes.

Constants

DEFAULT_CODER

Attributes

options[R]
silence[R]
silence?[R]

Public Class Methods

new(options = nil) click to toggle source

Creates a new cache. The options will be passed to any write method calls except for :namespace which can be used to set the global namespace for the cache.

# File lib/active_support/cache.rb, line 194
def initialize(options = nil)
  @options = options ? options.dup : {}
  @coder = @options.delete(:coder) { self.class::DEFAULT_CODER } || NullCoder
end

Private Class Methods

ensure_connection_pool_added!() click to toggle source
# File lib/active_support/cache.rb, line 183
def ensure_connection_pool_added!
  require "connection_pool"
rescue LoadError => e
  $stderr.puts "You don't have connection_pool installed in your application. Please add it to your Gemfile and run bundle install"
  raise e
end
retrieve_pool_options(options) click to toggle source
# File lib/active_support/cache.rb, line 176
def retrieve_pool_options(options)
  {}.tap do |pool_options|
    pool_options[:size] = options.delete(:pool_size) if options[:pool_size]
    pool_options[:timeout] = options.delete(:pool_timeout) if options[:pool_timeout]
  end
end

Public Instance Methods

cleanup(options = nil) click to toggle source

Cleanups the cache by removing expired entries.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

# File lib/active_support/cache.rb, line 547
def cleanup(options = nil)
  raise NotImplementedError.new("#{self.class.name} does not support cleanup")
end
clear(options = nil) click to toggle source

Clears the entire cache. Be careful with this method since it could affect other processes if shared cache is being used.

The options hash is passed to the underlying cache implementation.

Some implementations may not support this method.

# File lib/active_support/cache.rb, line 557
def clear(options = nil)
  raise NotImplementedError.new("#{self.class.name} does not support clear")
end
decrement(name, amount = 1, options = nil) click to toggle source

Decrements an integer value in the cache.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

# File lib/active_support/cache.rb, line 538
def decrement(name, amount = 1, options = nil)
  raise NotImplementedError.new("#{self.class.name} does not support decrement")
end
delete(name, options = nil) click to toggle source

Deletes an entry in the cache. Returns true if an entry is deleted.

Options are passed to the underlying cache implementation.

# File lib/active_support/cache.rb, line 483
def delete(name, options = nil)
  options = merged_options(options)

  instrument(:delete, name) do
    delete_entry(normalize_key(name, options), **options)
  end
end
delete_matched(matcher, options = nil) click to toggle source

Deletes all entries with keys matching the pattern.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

# File lib/active_support/cache.rb, line 520
def delete_matched(matcher, options = nil)
  raise NotImplementedError.new("#{self.class.name} does not support delete_matched")
end
delete_multi(names, options = nil) click to toggle source

Deletes multiple entries in the cache.

Options are passed to the underlying cache implementation.

# File lib/active_support/cache.rb, line 494
def delete_multi(names, options = nil)
  options = merged_options(options)
  names.map! { |key| normalize_key(key, options) }

  instrument :delete_multi, names do
    delete_multi_entries(names, **options)
  end
end
exist?(name, options = nil) click to toggle source

Returns true if the cache contains an entry for the given key.

Options are passed to the underlying cache implementation.

# File lib/active_support/cache.rb, line 506
def exist?(name, options = nil)
  options = merged_options(options)

  instrument(:exist?, name) do |payload|
    entry = read_entry(normalize_key(name, options), **options, event: payload)
    (entry && !entry.expired? && !entry.mismatched?(normalize_version(name, options))) || false
  end
end
fetch(name, options = nil, &block) click to toggle source

Fetches data from the cache, using the given key. If there is data in the cache with the given key, then that data is returned.

If there is no such data in the cache (a cache miss), then nil will be returned. However, if a block has been passed, that block will be passed the key and executed in the event of a cache miss. The return value of the block will be written to the cache under the given cache key, and that return value will be returned.

cache.write('today', 'Monday')
cache.fetch('today')  # => "Monday"

cache.fetch('city')   # => nil
cache.fetch('city') do
  'Duckburgh'
end
cache.fetch('city')   # => "Duckburgh"

You may also specify additional options via the options argument. Setting force: true forces a cache “miss,” meaning we treat the cache value as missing even if it's present. Passing a block is required when force is true so this always results in a cache write.

cache.write('today', 'Monday')
cache.fetch('today', force: true) { 'Tuesday' } # => 'Tuesday'
cache.fetch('today', force: true) # => ArgumentError

The :force option is useful when you're calling some other method to ask whether you should force a cache write. Otherwise, it's clearer to just call Cache#write.

Setting skip_nil: true will not cache nil result:

cache.fetch('foo') { nil }
cache.fetch('bar', skip_nil: true) { nil }
cache.exist?('foo') # => true
cache.exist?('bar') # => false

Setting compress: false disables compression of the cache entry.

Setting :expires_in will set an expiration time on the cache. All caches support auto-expiring content after a specified number of seconds. This value can be specified as an option to the constructor (in which case all entries will be affected), or it can be supplied to the fetch or write method to effect just one entry.

cache = ActiveSupport::Cache::MemoryStore.new(expires_in: 5.minutes)
cache.write(key, value, expires_in: 1.minute) # Set a lower value for one entry

Setting :version verifies the cache stored under name is of the same version. nil is returned on mismatches despite contents. This feature is used to support recyclable cache keys.

Setting :race_condition_ttl is very useful in situations where a cache entry is used very frequently and is under heavy load. If a cache expires and due to heavy load several different processes will try to read data natively and then they all will try to write to cache. To avoid that case the first process to find an expired cache entry will bump the cache expiration time by the value set in :race_condition_ttl. Yes, this process is extending the time for a stale value by another few seconds. Because of extended life of the previous cache, other processes will continue to use slightly stale data for a just a bit longer. In the meantime that first process will go ahead and will write into cache the new value. After that all the processes will start getting the new value. The key is to keep :race_condition_ttl small.

If the process regenerating the entry errors out, the entry will be regenerated after the specified number of seconds. Also note that the life of stale cache is extended only if it expired recently. Otherwise a new value is generated and :race_condition_ttl does not play any role.

# Set all values to expire after one minute.
cache = ActiveSupport::Cache::MemoryStore.new(expires_in: 1.minute)

cache.write('foo', 'original value')
val_1 = nil
val_2 = nil
sleep 60

Thread.new do
  val_1 = cache.fetch('foo', race_condition_ttl: 10.seconds) do
    sleep 1
    'new value 1'
  end
end

Thread.new do
  val_2 = cache.fetch('foo', race_condition_ttl: 10.seconds) do
    'new value 2'
  end
end

cache.fetch('foo') # => "original value"
sleep 10 # First thread extended the life of cache by another 10 seconds
cache.fetch('foo') # => "new value 1"
val_1 # => "new value 1"
val_2 # => "original value"

Other options will be handled by the specific cache store implementation. Internally, fetch calls read_entry, and calls write_entry on a cache miss. options will be passed to the read and write calls.

For example, MemCacheStore's write method supports the :raw option, which tells the memcached server to store all values as strings. We can use this option with fetch too:

cache = ActiveSupport::Cache::MemCacheStore.new
cache.fetch("foo", force: true, raw: true) do
  :bar
end
cache.fetch('foo') # => "bar"
# File lib/active_support/cache.rb, line 326
def fetch(name, options = nil, &block)
  if block_given?
    options = merged_options(options)
    key = normalize_key(name, options)

    entry = nil
    instrument(:read, name, options) do |payload|
      cached_entry = read_entry(key, **options, event: payload) unless options[:force]
      entry = handle_expired_entry(cached_entry, key, options)
      entry = nil if entry && entry.mismatched?(normalize_version(name, options))
      payload[:super_operation] = :fetch if payload
      payload[:hit] = !!entry if payload
    end

    if entry
      get_entry_value(entry, name, options)
    else
      save_block_result_to_cache(name, options, &block)
    end
  elsif options && options[:force]
    raise ArgumentError, "Missing block: Calling `Cache#fetch` with `force: true` requires a block."
  else
    read(name, options)
  end
end
fetch_multi(*names) { |name| ... } click to toggle source

Fetches data from the cache, using the given keys. If there is data in the cache with the given keys, then that data is returned. Otherwise, the supplied block is called for each key for which there was no data, and the result will be written to the cache and returned. Therefore, you need to pass a block that returns the data to be written to the cache. If you do not want to write the cache when the cache is not found, use read_multi.

Returns a hash with the data for each of the names. For example:

cache.write("bim", "bam")
cache.fetch_multi("bim", "unknown_key") do |key|
  "Fallback value for key: #{key}"
end
# => { "bim" => "bam",
#      "unknown_key" => "Fallback value for key: unknown_key" }

Options are passed to the underlying cache implementation. For example:

cache.fetch_multi("fizz", expires_in: 5.seconds) do |key|
  "buzz"
end
# => {"fizz"=>"buzz"}
cache.read("fizz")
# => "buzz"
sleep(6)
cache.read("fizz")
# => nil
# File lib/active_support/cache.rb, line 446
def fetch_multi(*names)
  raise ArgumentError, "Missing block: `Cache#fetch_multi` requires a block." unless block_given?

  options = names.extract_options!
  options = merged_options(options)

  instrument :read_multi, names, options do |payload|
    reads   = read_multi_entries(names, **options)
    writes  = {}
    ordered = names.index_with do |name|
      reads.fetch(name) { writes[name] = yield(name) }
    end

    payload[:hits] = reads.keys
    payload[:super_operation] = :fetch_multi

    write_multi(writes, options)

    ordered
  end
end
increment(name, amount = 1, options = nil) click to toggle source

Increments an integer value in the cache.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

# File lib/active_support/cache.rb, line 529
def increment(name, amount = 1, options = nil)
  raise NotImplementedError.new("#{self.class.name} does not support increment")
end
mute() { || ... } click to toggle source

Silences the logger within a block.

# File lib/active_support/cache.rb, line 206
def mute
  previous_silence, @silence = defined?(@silence) && @silence, true
  yield
ensure
  @silence = previous_silence
end
read(name, options = nil) click to toggle source

Reads data from the cache, using the given key. If there is data in the cache with the given key, then that data is returned. Otherwise, nil is returned.

Note, if data was written with the :expires_in or :version options, both of these conditions are applied before the data is returned.

Options are passed to the underlying cache implementation.

# File lib/active_support/cache.rb, line 361
def read(name, options = nil)
  options = merged_options(options)
  key     = normalize_key(name, options)
  version = normalize_version(name, options)

  instrument(:read, name, options) do |payload|
    entry = read_entry(key, **options, event: payload)

    if entry
      if entry.expired?
        delete_entry(key, **options)
        payload[:hit] = false if payload
        nil
      elsif entry.mismatched?(version)
        payload[:hit] = false if payload
        nil
      else
        payload[:hit] = true if payload
        entry.value
      end
    else
      payload[:hit] = false if payload
      nil
    end
  end
end
read_multi(*names) click to toggle source

Reads multiple values at once from the cache. Options can be passed in the last argument.

Some cache implementation may optimize this method.

Returns a hash mapping the names provided to the values found.

# File lib/active_support/cache.rb, line 394
def read_multi(*names)
  options = names.extract_options!
  options = merged_options(options)

  instrument :read_multi, names, options do |payload|
    read_multi_entries(names, **options, event: payload).tap do |results|
      payload[:hits] = results.keys
    end
  end
end
silence!() click to toggle source

Silences the logger.

# File lib/active_support/cache.rb, line 200
def silence!
  @silence = true
  self
end
write(name, value, options = nil) click to toggle source

Writes the value to the cache, with the key.

Options are passed to the underlying cache implementation.

# File lib/active_support/cache.rb, line 471
def write(name, value, options = nil)
  options = merged_options(options)

  instrument(:write, name, options) do
    entry = Entry.new(value, **options.merge(version: normalize_version(name, options)))
    write_entry(normalize_key(name, options), entry, **options)
  end
end
write_multi(hash, options = nil) click to toggle source

Cache Storage API to write multiple values at once.

# File lib/active_support/cache.rb, line 406
def write_multi(hash, options = nil)
  options = merged_options(options)

  instrument :write_multi, hash, options do |payload|
    entries = hash.each_with_object({}) do |(name, value), memo|
      memo[normalize_key(name, options)] = Entry.new(value, **options.merge(version: normalize_version(name, options)))
    end

    write_multi_entries entries, **options
  end
end

Private Instance Methods

delete_entry(key, **options) click to toggle source

Deletes an entry from the cache implementation. Subclasses must implement this method.

# File lib/active_support/cache.rb, line 630
def delete_entry(key, **options)
  raise NotImplementedError.new
end
delete_multi_entries(entries, **options) click to toggle source

Deletes multiples entries in the cache implementation. Subclasses MAY implement this method.

# File lib/active_support/cache.rb, line 636
def delete_multi_entries(entries, **options)
  entries.count { |key| delete_entry(key, **options) }
end
deserialize_entry(payload) click to toggle source
# File lib/active_support/cache.rb, line 597
def deserialize_entry(payload)
  payload.nil? ? nil : @coder.load(payload)
end
expanded_key(key) click to toggle source

Expands key to be a consistent string value. Invokes cache_key if object responds to cache_key. Otherwise, to_param method will be called. If the key is a Hash, then keys will be sorted alphabetically.

# File lib/active_support/cache.rb, line 690
def expanded_key(key)
  return key.cache_key.to_s if key.respond_to?(:cache_key)

  case key
  when Array
    if key.size > 1
      key.collect { |element| expanded_key(element) }
    else
      expanded_key(key.first)
    end
  when Hash
    key.collect { |k, v| "#{k}=#{v}" }.sort!
  else
    key
  end.to_param
end
expanded_version(key) click to toggle source
# File lib/active_support/cache.rb, line 711
def expanded_version(key)
  case
  when key.respond_to?(:cache_version) then key.cache_version.to_param
  when key.is_a?(Array)                then key.map { |element| expanded_version(element) }.tap(&:compact!).to_param
  when key.respond_to?(:to_a)          then expanded_version(key.to_a)
  end
end
get_entry_value(entry, name, options) click to toggle source
# File lib/active_support/cache.rb, line 745
def get_entry_value(entry, name, options)
  instrument(:fetch_hit, name, options) { }
  entry.value
end
handle_expired_entry(entry, key, options) click to toggle source
# File lib/active_support/cache.rb, line 729
def handle_expired_entry(entry, key, options)
  if entry && entry.expired?
    race_ttl = options[:race_condition_ttl].to_i
    if (race_ttl > 0) && (Time.now.to_f - entry.expires_at <= race_ttl)
      # When an entry has a positive :race_condition_ttl defined, put the stale entry back into the cache
      # for a brief period while the entry is being recalculated.
      entry.expires_at = Time.now + race_ttl
      write_entry(key, entry, expires_in: race_ttl * 2)
    else
      delete_entry(key, **options)
    end
    entry = nil
  end
  entry
end
instrument(operation, key, options = nil) { |payload| ... } click to toggle source
# File lib/active_support/cache.rb, line 719
def instrument(operation, key, options = nil)
  if logger && logger.debug? && !silence?
    logger.debug "Cache #{operation}: #{normalize_key(key, options)}#{options.blank? ? "" : " (#{options.inspect})"}"
  end

  payload = { key: key, store: self.class.name }
  payload.merge!(options) if options.is_a?(Hash)
  ActiveSupport::Notifications.instrument("cache_#{operation}.active_support", payload) { yield(payload) }
end
key_matcher(pattern, options) click to toggle source

Adds the namespace defined in the options to a pattern designed to match keys. Implementations that support delete_matched should call this method to translate a pattern that matches names into one that matches namespaced keys.

# File lib/active_support/cache.rb, line 566
def key_matcher(pattern, options) # :doc:
  prefix = options[:namespace].is_a?(Proc) ? options[:namespace].call : options[:namespace]
  if prefix
    source = pattern.source
    if source.start_with?("^")
      source = source[1, source.length]
    else
      source = ".*#{source[0, source.length]}"
    end
    Regexp.new("^#{Regexp.escape(prefix)}:#{source}", pattern.options)
  else
    pattern
  end
end
merged_options(call_options) click to toggle source

Merges the default options with ones specific to a method call.

# File lib/active_support/cache.rb, line 641
def merged_options(call_options)
  if call_options
    if options.empty?
      call_options
    else
      options.merge(call_options)
    end
  else
    options
  end
end
namespace_key(key, options = nil) click to toggle source

Prefix the key with a namespace string:

namespace_key 'foo', namespace: 'cache'
# => 'cache:foo'

With a namespace block:

namespace_key 'foo', namespace: -> { 'cache' }
# => 'cache:foo'
# File lib/active_support/cache.rb, line 668
def namespace_key(key, options = nil)
  options = merged_options(options)
  namespace = options[:namespace]

  if namespace.respond_to?(:call)
    namespace = namespace.call
  end

  if key && key.encoding != Encoding::UTF_8
    key = key.dup.force_encoding(Encoding::UTF_8)
  end

  if namespace
    "#{namespace}:#{key}"
  else
    key
  end
end
normalize_key(key, options = nil) click to toggle source

Expands and namespaces the cache key. May be overridden by cache stores to do additional normalization.

# File lib/active_support/cache.rb, line 655
def normalize_key(key, options = nil)
  namespace_key expanded_key(key), options
end
normalize_version(key, options = nil) click to toggle source
# File lib/active_support/cache.rb, line 707
def normalize_version(key, options = nil)
  (options && options[:version].try(:to_param)) || expanded_version(key)
end
read_entry(key, **options) click to toggle source

Reads an entry from the cache implementation. Subclasses must implement this method.

# File lib/active_support/cache.rb, line 583
def read_entry(key, **options)
  raise NotImplementedError.new
end
read_multi_entries(names, **options) click to toggle source

Reads multiple entries from the cache implementation. Subclasses MAY implement this method.

# File lib/active_support/cache.rb, line 603
def read_multi_entries(names, **options)
  names.each_with_object({}) do |name, results|
    key   = normalize_key(name, options)
    entry = read_entry(key, **options)

    next unless entry

    version = normalize_version(name, options)

    if entry.expired?
      delete_entry(key, **options)
    elsif !entry.mismatched?(version)
      results[name] = entry.value
    end
  end
end
save_block_result_to_cache(name, options) { |name| ... } click to toggle source
# File lib/active_support/cache.rb, line 750
def save_block_result_to_cache(name, options)
  result = instrument(:generate, name, options) do
    yield(name)
  end

  write(name, result, options) unless result.nil? && options[:skip_nil]
  result
end
serialize_entry(entry) click to toggle source
# File lib/active_support/cache.rb, line 593
def serialize_entry(entry)
  @coder.dump(entry)
end
write_entry(key, entry, **options) click to toggle source

Writes an entry to the cache implementation. Subclasses must implement this method.

# File lib/active_support/cache.rb, line 589
def write_entry(key, entry, **options)
  raise NotImplementedError.new
end
write_multi_entries(hash, **options) click to toggle source

Writes multiple entries to the cache implementation. Subclasses MAY implement this method.

# File lib/active_support/cache.rb, line 622
def write_multi_entries(hash, **options)
  hash.each do |key, entry|
    write_entry key, entry, **options
  end
end