Class: ActiveSupport::Cache::Store

Inherits:
Object
  • Object
show all
Defined in:
lib/active_support/cache.rb

Overview

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

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(options = nil) ⇒ Store

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.


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# 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

Instance Attribute Details

#optionsObject (readonly)

Returns the value of attribute options.


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# File 'lib/active_support/cache.rb', line 178

def options
  @options
end

#silenceObject (readonly) Also known as: silence?

Returns the value of attribute silence.


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# File 'lib/active_support/cache.rb', line 178

def silence
  @silence
end

Instance Method Details

#cleanup(options = nil) ⇒ Object

Cleans up the cache by removing expired entries.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

Raises:

  • (NotImplementedError)

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# 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) ⇒ Object

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.

Raises:

  • (NotImplementedError)

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# 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) ⇒ Object

Decrements an integer value in the cache.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

Raises:

  • (NotImplementedError)

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# 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) ⇒ Object

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

Options are passed to the underlying cache implementation.


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# 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) ⇒ Object

Deletes all entries with keys matching the pattern.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

Raises:

  • (NotImplementedError)

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# 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) ⇒ Object

Deletes multiple entries in the cache.

Options are passed to the underlying cache implementation.


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# 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) ⇒ Boolean

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

Options are passed to the underlying cache implementation.

Returns:

  • (Boolean)

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# 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) ⇒ Object

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"
    

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# 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) ⇒ Object

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

Raises:

  • (ArgumentError)

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# 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) ⇒ Object

Increments an integer value in the cache.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

Raises:

  • (NotImplementedError)

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# 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

#muteObject

Silences the logger within a block.


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# File 'lib/active_support/cache.rb', line 227

def mute
  previous_silence, @silence = defined?(@silence) && @silence, true
  yield
ensure
  @silence = previous_silence
end

#new_entry(value, options = nil) ⇒ Object

:nodoc:


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# File 'lib/active_support/cache.rb', line 546

def new_entry(value, options = nil) # :nodoc:
  Entry.new(value, **merged_options(options))
end

#read(name, options = nil) ⇒ Object

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.


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# 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) ⇒ Object

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.


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# 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!Object

Silences the logger.


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# File 'lib/active_support/cache.rb', line 221

def silence!
  @silence = true
  self
end

#write(name, value, options = nil) ⇒ Object

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.


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# 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) ⇒ Object

Cache Storage API to write multiple values at once.


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# 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