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:
-
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
- DEFAULT_CODER
- ESCAPE_KEY_CHARS
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 is defined, it will be used instead. Otherwise, MemCacheStore
will connect to localhost:11211 (the default memcached port).
ActiveSupport::Cache::Store::new
# File lib/active_support/cache/mem_cache_store.rb, line 86 def initialize(*addresses) addresses = addresses.flatten options = addresses.extract_options! 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 UNIVERSAL_OPTIONS.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 46 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 131 def clear(options = nil) rescue_error_with(nil) { @data.with { |c| c.flush_all } } end
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 120 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 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 107 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
Get the statistics from the memcached servers.
# File lib/active_support/cache/mem_cache_store.rb, line 136 def stats @data.with { |c| c.stats } end
Private Instance Methods
Delete an entry from the cache.
# File lib/active_support/cache/mem_cache_store.rb, line 180 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 199 def deserialize_entry(payload) entry = super entry = Entry.new(entry, compress: false) unless entry.nil? || entry.is_a?(Entry) entry 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 187 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, 213]}:md5:#{ActiveSupport::Digest.hexdigest(key)}" if key.size > 250 end key end
Read an entry from the cache.
# File lib/active_support/cache/mem_cache_store.rb, line 142 def read_entry(key, **options) rescue_error_with(nil) { deserialize_entry(@data.with { |c| c.get(key, options) }) } end
Reads multiple entries from the cache implementation.
# File lib/active_support/cache/mem_cache_store.rb, line 162 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) unless 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 205 def rescue_error_with(fallback) yield rescue Dalli::DalliError => e logger.error("DalliError (#{e}): #{e.message}") if logger fallback end
Write an entry to the cache.
# File lib/active_support/cache/mem_cache_store.rb, line 147 def write_entry(key, entry, **options) method = options[:unless_exist] ? :add : :set value = options[:raw] ? entry.value.to_s : serialize_entry(entry) 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 # The value "compress: false" prevents duplicate compression within Dalli. @data.with { |c| c.send(method, key, value, expires_in, **options, compress: false) } end end