class ActiveSupport::Cache::MemCacheStore
Memcached Cache Store¶ ↑
A cache store implementation which stores data in Memcached: memcached.org
This is currently the most popular cache store for production websites.
Special features:
-
Clustering and load balancing. One can specify multiple memcached servers, and
MemCacheStore
will load balance between all available servers. If a server goes down, thenMemCacheStore
will ignore it until it comes back up.
MemCacheStore
implements the Strategy::LocalCache
strategy which implements an in-memory cache inside of a block.
Constants
- ESCAPE_KEY_CHARS
- KEY_MAX_SIZE
- OVERRIDDEN_OPTIONS
These options represent behavior overridden by this implementation and should not be allowed to get down to the Dalli client
Public Class Methods
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). Passing a Dalli::Client
instance is deprecated and will be removed. Please pass an address instead.
ActiveSupport::Cache::Store::new
# File lib/active_support/cache/mem_cache_store.rb, line 118 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, address, or array of addresses." end if addresses.first.is_a?(Dalli::Client) ActiveSupport.deprecator.warn(<<~MSG) Initializing MemCacheStore with a Dalli::Client is deprecated and will be removed in Rails 7.2. Use memcached server addresses instead. MSG @data = addresses.first else @mem_cache_options = options.dup # The value "compress: false" prevents duplicate compression within Dalli. @mem_cache_options[:compress] = false (OVERRIDDEN_OPTIONS - %i(compress)).each { |name| @mem_cache_options.delete(name) } @data = self.class.build_mem_cache(*(addresses + [@mem_cache_options])) end end
Advertise cache versioning support.
# File lib/active_support/cache/mem_cache_store.rb, line 38 def self.supports_cache_versioning? true end
Public Instance Methods
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 215 def clear(options = nil) rescue_error_with(nil) { @data.with { |c| c.flush_all } } end
Decrement a cached integer value using the memcached decr atomic operator. Returns the updated value.
If the key is unset or has expired, it will be set to 0. Memcached does not support negative counters.
cache.decrement("foo") # => 0
To set a specific value, call write
passing raw: true
:
cache.write("baz", 5, raw: true) cache.decrement("baz") # => 4
Decrementing a non-numeric value, or a value written without raw: true
, will fail and return nil
.
# File lib/active_support/cache/mem_cache_store.rb, line 204 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], 0) } end end end
Increment a cached integer value using the memcached incr atomic operator. Returns the updated value.
If the key is unset or has expired, it will be set to amount
:
cache.increment("foo") # => 1 cache.increment("bar", 100) # => 100
To set a specific value, call write
passing raw: true
:
cache.write("baz", 5, raw: true) cache.increment("baz") # => 6
Incrementing a non-numeric value, or a value written without raw: true
, will fail and return nil
.
# File lib/active_support/cache/mem_cache_store.rb, line 180 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], amount) } end end end
# File lib/active_support/cache/mem_cache_store.rb, line 144 def inspect instance = @data || @mem_cache_options "#<#{self.class} options=#{options.inspect} mem_cache=#{instance.inspect}>" end
Get the statistics from the memcached servers.
# File lib/active_support/cache/mem_cache_store.rb, line 220 def stats @data.with { |c| c.stats } end
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 likeincrement
anddecrement
only on raw values. -
unless_exist: true
- Prevents overwriting an existing cache entry.
# File lib/active_support/cache/mem_cache_store.rb, line 150
Private Instance Methods
ActiveSupport::Cache::Store#default_serializer
# File lib/active_support/cache/mem_cache_store.rb, line 225 def default_serializer if Cache.format_version == 6.1 ActiveSupport.deprecator.warn <<~EOM Support for `config.active_support.cache_format_version = 6.1` has been deprecated and will be removed in Rails 7.2. Check the Rails upgrade guide at https://guides.rubyonrails.org/upgrading_ruby_on_rails.html#new-activesupport-cache-serialization-format for more information on how to upgrade. EOM Cache::SerializerWithFallback[:passthrough] else super end end
Delete an entry from the cache.
# File lib/active_support/cache/mem_cache_store.rb, line 288 def delete_entry(key, **options) rescue_error_with(false) { @data.with { |c| c.delete(key) } } end
ActiveSupport::Cache::Store#deserialize_entry
# File lib/active_support/cache/mem_cache_store.rb, line 319 def deserialize_entry(payload, raw: false, **) if payload && raw Entry.new(payload) else super(payload) end end
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.
ActiveSupport::Cache::Store#normalize_key
# File lib/active_support/cache/mem_cache_store.rb, line 303 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}" } if key.size > KEY_MAX_SIZE key_separator = ":hash:" key_hash = ActiveSupport::Digest.hexdigest(key) key_trim_size = KEY_MAX_SIZE - key_separator.size - key_hash.size key = "#{key[0, key_trim_size]}#{key_separator}#{key_hash}" end end key end
Read an entry from the cache.
# File lib/active_support/cache/mem_cache_store.rb, line 240 def read_entry(key, **options) deserialize_entry(read_serialized_entry(key, **options), **options) end
Reads multiple entries from the cache implementation.
# File lib/active_support/cache/mem_cache_store.rb, line 270 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.nil? || entry.expired? || entry.mismatched?(normalize_version(keys_to_names[key], options)) values[keys_to_names[key]] = entry.value end end values end
# File lib/active_support/cache/mem_cache_store.rb, line 244 def read_serialized_entry(key, **options) rescue_error_with(nil) do @data.with { |c| c.get(key, options) } end end
# File lib/active_support/cache/mem_cache_store.rb, line 327 def rescue_error_with(fallback) yield rescue Dalli::DalliError => error logger.error("DalliError (#{error}): #{error.message}") if logger ActiveSupport.error_reporter&.report( error, severity: :warning, source: "mem_cache_store.active_support", ) fallback end
ActiveSupport::Cache::Store#serialize_entry
# File lib/active_support/cache/mem_cache_store.rb, line 292 def serialize_entry(entry, raw: false, **options) if raw entry.value.to_s else super(entry, raw: raw, **options) end end
Write an entry to the cache.
# File lib/active_support/cache/mem_cache_store.rb, line 251 def write_entry(key, entry, **options) write_serialized_entry(key, serialize_entry(entry, **options), **options) end
# File lib/active_support/cache/mem_cache_store.rb, line 255 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