class ActiveSupport::Cache::MemCacheStore

A cache store implementation which stores data in Memcached: memcached.org

This is currently the most popular cache store for production websites.

Special features:

MemCacheStore implements the Strategy::LocalCache strategy which implements an in-memory cache inside of a block.

Constants

ESCAPE_KEY_CHARS

Public Class Methods

new(*addresses) click to toggle source

Creates a new MemCacheStore object, with the given memcached server addresses. Each address is either a host name, or a host-with-port string in the form of “host_name:port”. For example:

ActiveSupport::Cache::MemCacheStore.new("localhost", "server-downstairs.localnetwork:8229")

If no addresses are provided, but ENV['MEMCACHE_SERVERS'] is defined, it will be used instead. Otherwise, MemCacheStore will connect to localhost:11211 (the default memcached port).

Calls superclass method ActiveSupport::Cache::Store::new
# File lib/active_support/cache/mem_cache_store.rb, line 109
def initialize(*addresses)
  addresses = addresses.flatten
  options = addresses.extract_options!
  if options.key?(:cache_nils)
    options[:skip_nil] = !options.delete(:cache_nils)
  end
  super(options)

  unless [String, Dalli::Client, NilClass].include?(addresses.first.class)
    raise ArgumentError, "First argument must be an empty array, an array of hosts or a Dalli::Client instance."
  end
  if addresses.first.is_a?(Dalli::Client)
    @data = addresses.first
  else
    mem_cache_options = options.dup
    # The value "compress: false" prevents duplicate compression within Dalli.
    mem_cache_options[:compress] = false
    (UNIVERSAL_OPTIONS - %i(compress)).each { |name| mem_cache_options.delete(name) }
    @data = self.class.build_mem_cache(*(addresses + [mem_cache_options]))
  end
end
supports_cache_versioning?() click to toggle source

Advertise cache versioning support.

# File lib/active_support/cache/mem_cache_store.rb, line 30
def self.supports_cache_versioning?
  true
end

Public Instance Methods

clear(options = nil) click to toggle source

Clear the entire cache on all memcached servers. This method should be used with care when shared cache is being used.

# File lib/active_support/cache/mem_cache_store.rb, line 175
def clear(options = nil)
  rescue_error_with(nil) { @data.with { |c| c.flush_all } }
end
decrement(name, amount = 1, options = nil) click to toggle source

Decrement a cached value. This method uses the memcached decr atomic operator and can only be used on values written with the :raw option. Calling it on a value not stored with :raw will initialize that value to zero.

# File lib/active_support/cache/mem_cache_store.rb, line 164
def decrement(name, amount = 1, options = nil)
  options = merged_options(options)
  instrument(:decrement, name, amount: amount) do
    rescue_error_with nil do
      @data.with { |c| c.decr(normalize_key(name, options), amount, options[:expires_in]) }
    end
  end
end
increment(name, amount = 1, options = nil) click to toggle source

Increment a cached value. This method uses the memcached incr atomic operator and can only be used on values written with the :raw option. Calling it on a value not stored with :raw will initialize that value to zero.

# File lib/active_support/cache/mem_cache_store.rb, line 151
def increment(name, amount = 1, options = nil)
  options = merged_options(options)
  instrument(:increment, name, amount: amount) do
    rescue_error_with nil do
      @data.with { |c| c.incr(normalize_key(name, options), amount, options[:expires_in]) }
    end
  end
end
stats() click to toggle source

Get the statistics from the memcached servers.

# File lib/active_support/cache/mem_cache_store.rb, line 180
def stats
  @data.with { |c| c.stats }
end
write(name, value, options = nil) click to toggle source

Behaves the same as ActiveSupport::Cache::Store#write, but supports additional options specific to memcached.

Additional Options

  • raw: true - Sends the value directly to the server as raw bytes. The value must be a string or number. You can use memcached direct operations like increment and decrement only on raw values.

  • unless_exist: true - Prevents overwriting an existing cache entry.

# File lib/active_support/cache/mem_cache_store.rb, line 132
      

Private Instance Methods

default_coder() click to toggle source
# File lib/active_support/cache/mem_cache_store.rb, line 229
def default_coder
  Coders[Cache.format_version]
end
delete_entry(key, **options) click to toggle source

Delete an entry from the cache.

# File lib/active_support/cache/mem_cache_store.rb, line 282
def delete_entry(key, **options)
  rescue_error_with(false) { @data.with { |c| c.delete(key) } }
end
deserialize_entry(payload, raw: false, **) click to toggle source
# File lib/active_support/cache/mem_cache_store.rb, line 307
def deserialize_entry(payload, raw: false, **)
  if payload && raw
    Entry.new(payload)
  else
    super(payload)
  end
end
normalize_key(key, options) click to toggle source

Memcache keys are binaries. So we need to force their encoding to binary before applying the regular expression to ensure we are escaping all characters properly.

# File lib/active_support/cache/mem_cache_store.rb, line 297
def normalize_key(key, options)
  key = super
  if key
    key = key.dup.force_encoding(Encoding::ASCII_8BIT)
    key = key.gsub(ESCAPE_KEY_CHARS) { |match| "%#{match.getbyte(0).to_s(16).upcase}" }
    key = "#{key[0, 212]}:hash:#{ActiveSupport::Digest.hexdigest(key)}" if key.size > 250
  end
  key
end
read_entry(key, **options) click to toggle source

Read an entry from the cache.

# File lib/active_support/cache/mem_cache_store.rb, line 234
def read_entry(key, **options)
  deserialize_entry(read_serialized_entry(key, **options), **options)
end
read_multi_entries(names, **options) click to toggle source

Reads multiple entries from the cache implementation.

# File lib/active_support/cache/mem_cache_store.rb, line 264
def read_multi_entries(names, **options)
  keys_to_names = names.index_by { |name| normalize_key(name, options) }

  raw_values = @data.with { |c| c.get_multi(keys_to_names.keys) }
  values = {}

  raw_values.each do |key, value|
    entry = deserialize_entry(value, raw: options[:raw])

    unless entry.expired? || entry.mismatched?(normalize_version(keys_to_names[key], options))
      values[keys_to_names[key]] = entry.value
    end
  end

  values
end
read_serialized_entry(key, **options) click to toggle source
# File lib/active_support/cache/mem_cache_store.rb, line 238
def read_serialized_entry(key, **options)
  rescue_error_with(nil) do
    @data.with { |c| c.get(key, options) }
  end
end
rescue_error_with(fallback) { || ... } click to toggle source
# File lib/active_support/cache/mem_cache_store.rb, line 315
def rescue_error_with(fallback)
  yield
rescue Dalli::DalliError => error
  ActiveSupport.error_reporter&.report(error, handled: true, severity: :warning)
  logger.error("DalliError (#{error}): #{error.message}") if logger
  fallback
end
serialize_entry(entry, raw: false, **options) click to toggle source
# File lib/active_support/cache/mem_cache_store.rb, line 286
def serialize_entry(entry, raw: false, **options)
  if raw
    entry.value.to_s
  else
    super(entry, raw: raw, **options)
  end
end
write_entry(key, entry, **options) click to toggle source

Write an entry to the cache.

# File lib/active_support/cache/mem_cache_store.rb, line 245
def write_entry(key, entry, **options)
  write_serialized_entry(key, serialize_entry(entry, **options), **options)
end
write_serialized_entry(key, payload, **options) click to toggle source
# File lib/active_support/cache/mem_cache_store.rb, line 249
def write_serialized_entry(key, payload, **options)
  method = options[:unless_exist] ? :add : :set
  expires_in = options[:expires_in].to_i
  if options[:race_condition_ttl] && expires_in > 0 && !options[:raw]
    # Set the memcache expire a few minutes in the future to support race condition ttls on read
    expires_in += 5.minutes
  end
  rescue_error_with false do
    # Don't pass compress option to Dalli since we are already dealing with compression.
    options.delete(:compress)
    @data.with { |c| c.send(method, key, payload, expires_in, **options) }
  end
end