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

Methods

Attributes

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

Class Public methods

new(options = nil)

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.

📝 Source code 
# File activesupport/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
🔎 See on GitHub

Instance Public methods

cleanup(options = nil)

Cleans up the cache by removing expired entries.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

📝 Source code 
# File activesupport/lib/active_support/cache.rb, line 582
      def cleanup(options = nil)
        raise NotImplementedError.new("#{self.class.name} does not support cleanup")
      end
🔎 See on GitHub

clear(options = nil)

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.

📝 Source code 
# File activesupport/lib/active_support/cache.rb, line 592
      def clear(options = nil)
        raise NotImplementedError.new("#{self.class.name} does not support clear")
      end
🔎 See on GitHub

decrement(name, amount = 1, options = nil)

Decrements an integer value in the cache.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

📝 Source code 
# File activesupport/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
🔎 See on GitHub

delete(name, options = nil)

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

Options are passed to the underlying cache implementation.

📝 Source code 
# File activesupport/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
🔎 See on GitHub

delete_matched(matcher, options = nil)

Deletes all entries with keys matching the pattern.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

📝 Source code 
# File activesupport/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
🔎 See on GitHub

delete_multi(names, options = nil)

Deletes multiple entries in the cache.

Options are passed to the underlying cache implementation.

📝 Source code 
# File activesupport/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
🔎 See on GitHub

exist?(name, options = nil)

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

Options are passed to the underlying cache implementation.

📝 Source code 
# File activesupport/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
🔎 See on GitHub

fetch(name, options = nil, &block)

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"
📝 Source code 
# File activesupport/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
🔎 See on GitHub

fetch_multi(*names)

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
📝 Source code 
# File activesupport/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
🔎 See on GitHub

increment(name, amount = 1, options = nil)

Increments an integer value in the cache.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

📝 Source code 
# File activesupport/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
🔎 See on GitHub

mute()

Silences the logger within a block.

📝 Source code 
# File activesupport/lib/active_support/cache.rb, line 227
      def mute
        previous_silence, @silence = defined?(@silence) && @silence, true
        yield
      ensure
        @silence = previous_silence
      end
🔎 See on GitHub

read(name, options = nil)

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.

📝 Source code 
# File activesupport/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
🔎 See on GitHub

read_multi(*names)

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.

📝 Source code 
# File activesupport/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
🔎 See on GitHub

silence!()

Silences the logger.

📝 Source code 
# File activesupport/lib/active_support/cache.rb, line 221
      def silence!
        @silence = true
        self
      end
🔎 See on GitHub

write(name, value, options = nil)

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.

📝 Source code 
# File activesupport/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
🔎 See on GitHub

write_multi(hash, options = nil)

Cache Storage API to write multiple values at once.

📝 Source code 
# File activesupport/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
🔎 See on GitHub

Instance Private methods

key_matcher(pattern, options)

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.

📝 Source code 
# File activesupport/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
🔎 See on GitHub