class ActiveSupport::Cache::Store - activesupport-4.2.3 Documentation

# 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

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

:deprecated:

    # File lib/active_support/cache.rb, line 189
    def self.instrument
      ActiveSupport::Deprecation.warn "ActiveSupport::Cache.instrument is deprecated and will be removed in Rails 5. Instrumentation is now always on so you can safely stop using it."
      true
    end

instrument=(boolean) click to toggle source

:deprecated:

    # File lib/active_support/cache.rb, line 183
    def self.instrument=(boolean)
      ActiveSupport::Deprecation.warn "ActiveSupport::Cache.instrument= is deprecated and will be removed in Rails 5. Instrumentation is now always on so you can safely stop using it."
      true
    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 164
    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 450
    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.

The options hash is passed to the underlying cache implementation.

All implementations may not support this method.

    # File lib/active_support/cache.rb, line 460
    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

Decrement 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 441
    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 398
    def delete(name, options = nil)
      options = merged_options(options)

      instrument(:delete, name) do
        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 423
    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

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 409
    def exist?(name, options = nil)
      options = merged_options(options)

      instrument(:exist?, name) do
        entry = read_entry(namespaced_key(name, options), options)
        (entry && !entry.expired?) || false
      end
    end

fetch(name, options = nil) { |_name| ... } 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` 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 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) 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 288
    def fetch(name, options = nil)
      if block_given?
        options = merged_options(options)
        key = namespaced_key(name, options)

        cached_entry = find_cached_entry(key, name, options) unless options[:force]
        entry = handle_expired_entry(cached_entry, key, options)

        if entry
          get_entry_value(entry, name, options)
        else
          save_block_result_to_cache(name, options) { |_name| yield _name }
        end
      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.

Options are passed to the underlying cache implementation.

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

    cache.write("bim", "bam")
    cache.fetch_multi("bim", "boom") { |key| key * 2 }
    # => { "bam" => "bam", "boom" => "boomboom" }

    # File lib/active_support/cache.rb, line 369
    def fetch_multi(*names)
      options = names.extract_options!
      options = merged_options(options)
      results = read_multi(*names, options)

      names.each_with_object({}) do |name, memo|
        memo[name] = results.fetch(name) do
          value = yield name
          write(name, value, options)
          value
        end
      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 432
    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 175
    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 311
    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 338
    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 169
    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 386
    def write(name, value, options = nil)
      options = merged_options(options)

      instrument(:write, name, options) do
        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 469
    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

### Private Instance Methods

find_cached_entry(key, name, options) click to toggle source

    # File lib/active_support/cache.rb, line 555
    def find_cached_entry(key, name, options)
      instrument(:read, name, options) do |payload|
        payload[:super_operation] = :fetch if payload
        read_entry(key, options)
      end
    end

get_entry_value(entry, name, options) click to toggle source

    # File lib/active_support/cache.rb, line 578
    def get_entry_value(entry, name, options)
      instrument(:fetch_hit, name, options) { |payload| }
      entry.value
    end

handle_expired_entry(entry, key, options) click to toggle source

    # File lib/active_support/cache.rb, line 562
    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 :race_condition_ttl defined, put the stale entry back into the cache
          # for a brief period while the entry is begin 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 542
    def instrument(operation, key, options = nil)
      log(operation, key, options)

      payload = { :key => key }
      payload.merge!(options) if options.is_a?(Hash)
      ActiveSupport::Notifications.instrument("cache_#{operation}.active_support", payload){ yield(payload) }
    end

log(operation, key, options = nil) click to toggle source

    # File lib/active_support/cache.rb, line 550
    def log(operation, key, options = nil)
      return unless logger && logger.debug? && !silence?
      logger.debug("Cache #{operation}: #{key}#{options.blank? ? "" : " (#{options.inspect})"}")
    end

namespaced_key(key, options) click to toggle source

Prefix a key with the namespace. Namespace and key will be delimited with a colon.

    # File lib/active_support/cache.rb, line 534
    def namespaced_key(key, options)
      key = expanded_key(key)
      namespace = options[:namespace] if options
      prefix = namespace.is_a?(Proc) ? namespace.call : namespace
      key = "#{prefix}:#{key}" if prefix
      key
    end

save_block_result_to_cache(name, options) { |name| ... } click to toggle source

    # File lib/active_support/cache.rb, line 583
    def save_block_result_to_cache(name, options)
      result = instrument(:generate, name, options) do |payload|
        yield(name)
      end

      write(name, result, options)
      result
    end