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

Caches can also store values in a compressed format to save space and reduce time spent sending data. Since there is overhead, values must be large enough to warrant compression. To turn on compression either pass `:compress => true` in the initializer or as an option to `fetch` or `write`. To specify the threshold at which to compress values, set the `:compress_threshold` option. The default threshold is 16K.

### Attributes

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

### Public Class Methods

instrument() click to toggle source

    # File lib/active_support/cache.rb, line 175
    def self.instrument
      Thread.current[:instrument_cache_store] || false
    end

instrument=(boolean) click to toggle source

Set to true if cache stores should be instrumented. Default is false.

    # File lib/active_support/cache.rb, line 171
    def self.instrument=(boolean)
      Thread.current[:instrument_cache_store] = boolean
    end

new(options = nil) click to toggle source

Create 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 152
    def initialize(options = nil)
      @options = options ? options.dup : {}
    end

### Public Instance Methods

cleanup(options = nil) click to toggle source

Cleanup the cache by removing expired entries.

Options are passed to the underlying cache implementation.

All implementations may not support this method.

    # File lib/active_support/cache.rb, line 425
    def cleanup(options = nil)
      raise NotImplementedError.new("#{self.class.name} does not support cleanup")
    end

clear(options = nil) click to toggle source

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

Options are passed to the underlying cache implementation.

All implementations may not support this method.

    # File lib/active_support/cache.rb, line 435
    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

Increment an integer value in the cache.

Options are passed to the underlying cache implementation.

All implementations may not support this method.

    # File lib/active_support/cache.rb, line 416
    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 371
    def delete(name, options = nil)
      options = merged_options(options)
      instrument(:delete, name) do |payload|
        delete_entry(namespaced_key(name, options), options)
      end
    end

delete_matched(matcher, options = nil) click to toggle source

Delete all entries with keys matching the pattern.

Options are passed to the underlying cache implementation.

All implementations may not support this method.

    # File lib/active_support/cache.rb, line 398
    def delete_matched(matcher, options = nil)
      raise NotImplementedError.new("#{self.class.name} does not support delete_matched")
    end

exist?(name, options = nil) click to toggle source

Return 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 381
    def exist?(name, options = nil)
      options = merged_options(options)
      instrument(:exist?, name) do |payload|
        entry = read_entry(namespaced_key(name, options), options)
        if entry && !entry.expired?
          true
        else
          false
        end
      end
    end

fetch(name, options = nil) { || ... } 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 run 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` will force a cache miss:

    cache.write("today", "Monday")
    cache.fetch("today", :force => true)  # => nil

Setting `:compress` will store a large cache entry set by the call in a compressed format.

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 `: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 seven 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 big 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 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) do
        sleep 1
        "new value 1"
      end
    end

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

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

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 271
    def fetch(name, options = nil)
      if block_given?
        options = merged_options(options)
        key = namespaced_key(name, options)
        unless options[:force]
          entry = instrument(:read, name, options) do |payload|
            payload[:super_operation] = :fetch if payload
            read_entry(key, options)
          end
        end
        if entry && entry.expired?
          race_ttl = options[:race_condition_ttl].to_f
          if race_ttl and Time.now.to_f - entry.expires_at <= race_ttl
            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

        if entry
          instrument(:fetch_hit, name, options) { |payload| }
          entry.value
        else
          result = instrument(:generate, name, options) do |payload|
            yield
          end
          write(name, result, options)
          result
        end
      else
        read(name, options)
      end
    end

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

Increment an integer value in the cache.

Options are passed to the underlying cache implementation.

All implementations may not support this method.

    # File lib/active_support/cache.rb, line 407
    def increment(name, amount = 1, options = nil)
      raise NotImplementedError.new("#{self.class.name} does not support increment")
    end

mute() { || ... } click to toggle source

Silence the logger within a block.

    # File lib/active_support/cache.rb, line 163
    def mute
      previous_silence, @silence = defined?(@silence) && @silence, true
      yield
    ensure
      @silence = previous_silence
    end

read(name, options = nil) 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. Otherwise, nil is returned.

Options are passed to the underlying cache implementation.

    # File lib/active_support/cache.rb, line 312
    def read(name, options = nil)
      options = merged_options(options)
      key = namespaced_key(name, options)
      instrument(:read, name, options) do |payload|
        entry = read_entry(key, options)
        if entry
          if entry.expired?
            delete_entry(key, options)
            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

Read 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 339
    def read_multi(*names)
      options = names.extract_options!
      options = merged_options(options)
      results = {}
      names.each do |name|
        key = namespaced_key(name, options)
        entry = read_entry(key, options)
        if entry
          if entry.expired?
            delete_entry(key, options)
          else
            results[name] = entry.value
          end
        end
      end
      results
    end

silence!() click to toggle source

Silence the logger.

    # File lib/active_support/cache.rb, line 157
    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 360
    def write(name, value, options = nil)
      options = merged_options(options)
      instrument(:write, name, options) do |payload|
        entry = Entry.new(value, options)
        write_entry(namespaced_key(name, options), entry, options)
      end
    end

### Protected Instance Methods

key_matcher(pattern, options) click to toggle source

Add 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 443
    def key_matcher(pattern, options)
      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