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
Public Class Methods
Creates 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 161 def initialize(options = nil) @options = options ? options.dup : {} end
Public Instance Methods
Cleanups 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 459 def cleanup(options = nil) raise NotImplementedError.new("#{self.class.name} does not support cleanup") end
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.
All implementations may not support this method.
# File lib/active_support/cache.rb, line 469 def clear(options = nil) raise NotImplementedError.new("#{self.class.name} does not support clear") end
Decrements 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 450 def decrement(name, amount = 1, options = nil) raise NotImplementedError.new("#{self.class.name} does not support decrement") end
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 407 def delete(name, options = nil) options = merged_options(options) instrument(:delete, name) do delete_entry(normalize_key(name, options), options) end end
Deletes 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 432 def delete_matched(matcher, options = nil) raise NotImplementedError.new("#{self.class.name} does not support delete_matched") end
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 418 def exist?(name, options = nil) options = merged_options(options) instrument(:exist?, name) do entry = read_entry(normalize_key(name, options), options) (entry && !entry.expired?) || false end end
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
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 Cache#write
.
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.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"
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 281 def fetch(name, options = nil) 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) unless options[:force] entry = handle_expired_entry(cached_entry, key, 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) { |_name| yield _name } end elsif options && options[:force] raise ArgumentError, "Missing block: Calling `Cache#fetch` with `force: true` requires a block." else read(name, options) end end
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.
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", "unknown_key") do |key| "Fallback value for key: #{key}" end # => { "bim" => "bam", # "unknown_key" => "Fallback value for key: unknown_key" }
# File lib/active_support/cache.rb, line 376 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) 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
Increments 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 increment(name, amount = 1, options = nil) raise NotImplementedError.new("#{self.class.name} does not support increment") end
Silences the logger within a block.
# File lib/active_support/cache.rb, line 172 def mute previous_silence, @silence = defined?(@silence) && @silence, true yield ensure @silence = previous_silence end
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 = normalize_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
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.
# 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 = normalize_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
Silences the logger.
# File lib/active_support/cache.rb, line 166 def silence! @silence = true self end
Writes the value to the cache, with the key.
Options are passed to the underlying cache implementation.
# File lib/active_support/cache.rb, line 395 def write(name, value, options = nil) options = merged_options(options) instrument(:write, name, options) do entry = Entry.new(value, options) write_entry(normalize_key(name, options), entry, options) end end
Private Instance Methods
Deletes an entry from the cache implementation. Subclasses must implement this method.
# File lib/active_support/cache.rb, line 507 def delete_entry(key, options) raise NotImplementedError.new end
Expands key to be a consistent string value. Invokes cache_key
if object responds to cache_key
. Otherwise,
to_param
method will be called. If the key is a Hash, then keys will be sorted alphabetically.
# File lib/active_support/cache.rb, line 523 def expanded_key(key) return key.cache_key.to_s if key.respond_to?(:cache_key) case key when Array if key.size > 1 key = key.collect { |element| expanded_key(element) } else key = key.first end when Hash key = key.sort_by { |k, _| k.to_s }.collect { |k, v| "#{k}=#{v}" } end key.to_param end
# File lib/active_support/cache.rb, line 579 def get_entry_value(entry, name, options) instrument(:fetch_hit, name, options) {} entry.value end
# File lib/active_support/cache.rb, line 563 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 a positive :race_condition_ttl defined, put the stale entry back into the cache # for a brief period while the entry is being 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
# File lib/active_support/cache.rb, line 550 def instrument(operation, key, options = nil) log { "Cache #{operation}: #{normalize_key(key, options)}#{options.blank? ? "" : " (#{options.inspect})"}" } payload = { key: key } payload.merge!(options) if options.is_a?(Hash) ActiveSupport::Notifications.instrument("cache_#{operation}.active_support", payload) { yield(payload) } end
Adds 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 478 def key_matcher(pattern, options) # :doc: 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
# File lib/active_support/cache.rb, line 558 def log return unless logger && logger.debug? && !silence? logger.debug(yield) end
Merges the default options with ones specific to a method call.
# File lib/active_support/cache.rb, line 512 def merged_options(call_options) if call_options options.merge(call_options) else options.dup end end
Prefixes a key with the namespace. Namespace and key will be delimited with a colon.
# File lib/active_support/cache.rb, line 542 def normalize_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
Reads an entry from the cache implementation. Subclasses must implement this method.
# File lib/active_support/cache.rb, line 495 def read_entry(key, options) raise NotImplementedError.new end
# File lib/active_support/cache.rb, line 584 def save_block_result_to_cache(name, options) result = instrument(:generate, name, options) do yield(name) end write(name, result, options) result end
Writes an entry to the cache implementation. Subclasses must implement this method.
# File lib/active_support/cache.rb, line 501 def write_entry(key, entry, options) raise NotImplementedError.new end