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 Ruby object that is supported by its coder's dump and load methods.

cache = ActiveSupport::Cache::MemoryStore.new

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

cache.write('not serializable', Proc.new {}) # => TypeError

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

Attributes

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

Public Class Methods

new(options = nil) click to toggle source

Creates a new cache.

Options

  • :namespace - Sets the namespace for the cache. This option is especially useful if your application shares a cache with other applications.

  • :coder - Replaces the default cache entry serialization mechanism with a custom one. The coder must respond to dump and load. Using a custom coder disables automatic compression.

Any other specified options are treated as default options for the relevant cache operations, such as read, write, and fetch.

# File lib/active_support/cache.rb, line 211
def initialize(options = nil)
  @options = options ? normalize_options(options) : {}
  @options[:compress] = true unless @options.key?(:compress)
  @options[:compress_threshold] = DEFAULT_COMPRESS_LIMIT unless @options.key?(:compress_threshold)

  @coder = @options.delete(:coder) { default_coder } || NullCoder
  @coder_supports_compression = @coder.respond_to?(:dump_compressed)
end

Private Class Methods

ensure_connection_pool_added!() click to toggle source
# File lib/active_support/cache.rb, line 190
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 183
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

Cleans up 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 582
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 592
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 573
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 514
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 555
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 525
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 537
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"

Options

Internally, fetch calls read_entry, and calls write_entry on a cache miss. Thus, fetch supports the same options as read and write. Additionally, fetch supports the following options:

  • 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 write.

  • skip_nil: true - Prevents caching a nil result:

    cache.fetch('foo') { nil }
    cache.fetch('bar', skip_nil: true) { nil }
    cache.exist?('foo') # => true
    cache.exist?('bar') # => false
    
  • :race_condition_ttl - Specifies the number of seconds during which an expired value can be reused while a new value is being generated. This can be used to prevent race conditions when cache entries expire, by preventing multiple processes from simultaneously regenerating the same entry (also known as the dog pile effect).

    When a process encounters a cache entry that has expired less than :race_condition_ttl seconds ago, it will bump the expiration time by :race_condition_ttl seconds before generating a new value. During this extended time window, while the process generates a new value, other processes will continue to use the old value. After the first process writes the new value, other processes will then use it.

    If the first process errors out while generating a new value, another process can try to generate a new value after the extended time window has elapsed.

    # 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"
    
# File lib/active_support/cache.rb, line 321
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 447
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 564
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 227
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

  • :version - Specifies a version for the cache entry. If the cached version does not match the requested version, the read will be treated as a cache miss. This feature is used to support recyclable cache keys.

Other options will be handled by the specific cache store implementation.

# File lib/active_support/cache.rb, line 362
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 395
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 221
def silence!
  @silence = true
  self
end
write(name, value, options = nil) click to toggle source

Writes the value to the cache with the key. The value must be supported by the coder's dump and load methods.

By default, cache entries larger than 1kB are compressed. Compression allows more data to be stored in the same memory footprint, leading to fewer cache evictions and higher hit rates.

Options

  • compress: false - Disables compression of the cache entry.

  • :compress_threshold - The compression threshold, specified in bytes. Cache entries larger than this threshold will be compressed. Defaults to 1.kilobyte.

  • :expires_in - Sets a relative expiration time for the cache entry, specified in seconds. :expire_in and :expired_in are aliases for :expires_in.

    cache = ActiveSupport::Cache::MemoryStore.new(expires_in: 5.minutes)
    cache.write(key, value, expires_in: 1.minute) # Set a lower value for one entry
    
  • :expires_at - Sets an absolute expiration time for the cache entry.

    cache = ActiveSupport::Cache::MemoryStore.new
    cache.write(key, value, expires_at: Time.now.at_end_of_hour)
    
  • :version - Specifies a version for the cache entry. When reading from the cache, if the cached version does not match the requested version, the read will be treated as a cache miss. This feature is used to support recyclable cache keys.

Other options will be handled by the specific cache store implementation.

# File lib/active_support/cache.rb, line 502
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 407
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

default_coder() click to toggle source
# File lib/active_support/cache.rb, line 597
def default_coder
  Coders[Cache.format_version]
end
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 674
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 680
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 641
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 747
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 768
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 802
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 786
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.to_f + 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 776
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 605
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 685
def merged_options(call_options)
  if call_options
    call_options = normalize_options(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 725
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 712
def normalize_key(key, options = nil)
  namespace_key expanded_key(key), options
end
normalize_options(options) click to toggle source

Normalize aliased options to their canonical form

# File lib/active_support/cache.rb, line 699
def normalize_options(options)
  options = options.dup
  OPTION_ALIASES.each do |canonical_name, aliases|
    alias_key = aliases.detect { |key| options.key?(key) }
    options[canonical_name] ||= options[alias_key] if alias_key
    options.except!(*aliases)
  end

  options
end
normalize_version(key, options = nil) click to toggle source
# File lib/active_support/cache.rb, line 764
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 622
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 647
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 807
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, **options) click to toggle source
# File lib/active_support/cache.rb, line 632
def serialize_entry(entry, **options)
  options = merged_options(options)
  if @coder_supports_compression && options[:compress]
    @coder.dump_compressed(entry, options[:compress_threshold] || DEFAULT_COMPRESS_LIMIT)
  else
    @coder.dump(entry)
  end
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 628
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 666
def write_multi_entries(hash, **options)
  hash.each do |key, entry|
    write_entry key, entry, **options
  end
end