Active Support 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 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") # => true
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
- C
- D
- E
- F
- I
- K
- M
- N
- R
- S
- W
Attributes
[R] | options | |
[R] | silence | |
[R] | silence? |
Class Public methods
new(options = nil) Link
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.
:serializer
-
The serializer for cached values. Must respond to
dump
andload
.The default serializer depends on the cache format version (set via
config.active_support.cache_format_version
when usingRails
). The default serializer for each format version includes a fallback mechanism to deserialize values from any format version. This behavior makes it easy to migrate between format versions without invalidating the entire cache.You can also specify
serializer: :message_pack
to use a preconfigured serializer based onActiveSupport::MessagePack
. The:message_pack
serializer includes the same deserialization fallback mechanism, allowing easy migration from (or to) the default serializer. The:message_pack
serializer may improve performance, but it requires themsgpack
gem. :compressor
-
The compressor for serialized cache values. Must respond to
deflate
andinflate
.The default compressor is
Zlib
. To define a new custom compressor that also decompresses old cache entries, you can check compressed values for Zlib’s"\x78"
signature:module MyCompressor def self.deflate(dumped) # compression logic... (make sure result does not start with "\x78"!) end def self.inflate(compressed) if compressed.start_with?("\x78") Zlib.inflate(compressed) else # decompression logic... end end end ActiveSupport::Cache.lookup_store(:redis_cache_store, compressor: MyCompressor)
:coder
-
The coder for serializing and (optionally) compressing cache entries. Must respond to
dump
andload
.The default coder composes the serializer and compressor, and includes some performance optimizations. If you only need to override the serializer or compressor, you should specify the
:serializer
or:compressor
options instead.If the store can handle cache entries directly, you may also specify
coder: nil
to omit the serializer, compressor, and coder. For example, if you are usingActiveSupport::Cache::MemoryStore
and can guarantee that cache values will not be mutated, you can specifycoder: nil
to avoid the overhead of safeguarding against mutation.The
:coder
option is mutally exclusive with the:serializer
and:compressor
options. Specifying them together will raise anArgumentError
.
Any other specified options are treated as default options for the relevant cache operations, such as read
, write
, and fetch
.
# File activesupport/lib/active_support/cache.rb, line 295 def initialize(options = nil) @options = options ? validate_options(normalize_options(options)) : {} @options[:compress] = true unless @options.key?(:compress) @options[:compress_threshold] ||= DEFAULT_COMPRESS_LIMIT @coder = @options.delete(:coder) do legacy_serializer = Cache.format_version < 7.1 && !@options[:serializer] serializer = @options.delete(:serializer) || default_serializer serializer = Cache::SerializerWithFallback[serializer] if serializer.is_a?(Symbol) compressor = @options.delete(:compressor) { Zlib } Cache::Coder.new(serializer, compressor, legacy_serializer: legacy_serializer) end @coder ||= Cache::SerializerWithFallback[:passthrough] @coder_supports_compression = @coder.respond_to?(:dump_compressed) end
Instance Public methods
cleanup(options = nil) Link
Cleans up the cache by removing expired entries.
Options are passed to the underlying cache implementation.
Some implementations may not support this method.
clear(options = nil) Link
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.
decrement(name, amount = 1, options = nil) Link
Decrements an integer value in the cache.
Options are passed to the underlying cache implementation.
Some implementations may not support this method.
delete(name, options = nil) Link
Deletes an entry in the cache. Returns true
if an entry is deleted and false
otherwise.
Options are passed to the underlying cache implementation.
delete_matched(matcher, options = nil) Link
Deletes all entries with keys matching the pattern.
Options are passed to the underlying cache implementation.
Some implementations may not support this method.
delete_multi(names, options = nil) Link
Deletes multiple entries in the cache. Returns the number of deleted entries.
Options are passed to the underlying cache implementation.
# File activesupport/lib/active_support/cache.rb, line 687 def delete_multi(names, options = nil) return 0 if names.empty? options = merged_options(options) names.map! { |key| normalize_key(key, options) } instrument_multi :delete_multi, names do delete_multi_entries(names, **options) end end
exist?(name, options = nil) Link
Returns true
if the cache contains an entry for the given key.
Options are passed to the underlying cache implementation.
# File activesupport/lib/active_support/cache.rb, line 701 def exist?(name, options = nil) options = merged_options(options) key = normalize_key(name, options) instrument(:exist?, key) do |payload| entry = read_entry(key, **options, event: payload) (entry && !entry.expired? && !entry.mismatched?(normalize_version(name, options))) || false end end
fetch(name, options = nil, &block) Link
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 whenforce
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 callwrite
. -
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) cache.write("foo", "original value") val_1 = nil val_2 = nil p cache.read("foo") # => "original value" sleep 1 # wait until the cache expires t1 = Thread.new do # fetch does the following: # 1. gets an recent expired entry # 2. extends the expiry by 2 seconds (race_condition_ttl) # 3. regenerates the new value val_1 = cache.fetch("foo", race_condition_ttl: 2) do sleep 1 "new value 1" end end # Wait until t1 extends the expiry of the entry # but before generating the new value sleep 0.1 val_2 = cache.fetch("foo", race_condition_ttl: 2) do # This block won't be executed because t1 extended the expiry "new value 2" end t1.join p val_1 # => "new value 1" p val_2 # => "oritinal value" p cache.fetch("foo") # => "new value 1" # The entry requires 3 seconds to expire (expires_in + race_condition_ttl) # We have waited 2 seconds already (sleep(1) + t1.join) thus we need to wait 1 # more second to see the entry expire. sleep 1 p cache.fetch("foo") # => nil
Dynamic Options
In some cases it may be necessary to dynamically compute options based on the cached value. To support this, an ActiveSupport::Cache::WriteOptions
instance is passed as the second argument to the block. For example:
cache.fetch("authentication-token:#{user.id}") do |key, options|
token = authenticate_to_service
options.expires_at = token.expires_at
token
end
# File activesupport/lib/active_support/cache.rb, line 444 def fetch(name, options = nil, &block) if block_given? options = merged_options(options) key = normalize_key(name, options) entry = nil unless options[:force] instrument(:read, key, options) do |payload| cached_entry = read_entry(key, **options, event: payload) entry = handle_expired_entry(cached_entry, key, options) if entry if entry.mismatched?(normalize_version(name, options)) entry = nil else begin entry.value rescue DeserializationError entry = nil end end end payload[:super_operation] = :fetch if payload payload[:hit] = !!entry if payload end end if entry get_entry_value(entry, name, options) else save_block_result_to_cache(name, key, 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) Link
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" }
You may also specify additional options via the options
argument. See fetch
for details. Other 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
# File activesupport/lib/active_support/cache.rb, line 593 def fetch_multi(*names) raise ArgumentError, "Missing block: `Cache#fetch_multi` requires a block." unless block_given? return {} if names.empty? options = names.extract_options! options = merged_options(options) writes = {} ordered = instrument_multi :read_multi, names, options do |payload| if options[:force] reads = {} else reads = read_multi_entries(names, **options) end ordered = names.index_with do |name| reads.fetch(name) { writes[name] = yield(name) } end writes.compact! if options[:skip_nil] payload[:hits] = reads.keys payload[:super_operation] = :fetch_multi ordered end write_multi(writes, options) ordered end
increment(name, amount = 1, options = nil) Link
Increments an integer value in the cache.
Options are passed to the underlying cache implementation.
Some implementations may not support this method.
mute() Link
Silences the logger within a block.
read(name, options = nil) Link
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
-
:namespace
- Replace the store namespace for this call. -
: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.
# File activesupport/lib/active_support/cache.rb, line 498 def read(name, options = nil) options = merged_options(options) key = normalize_key(name, options) version = normalize_version(name, options) instrument(:read, key, 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 begin entry.value rescue DeserializationError payload[:hit] = false nil end end else payload[:hit] = false if payload nil end end end
read_multi(*names) Link
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 activesupport/lib/active_support/cache.rb, line 536 def read_multi(*names) return {} if names.empty? options = names.extract_options! options = merged_options(options) instrument_multi :read_multi, names, options do |payload| read_multi_entries(names, **options, event: payload).tap do |results| payload[:hits] = results.keys end end end
silence!() Link
Silences the logger.
write(name, value, options = nil) Link
Writes the value to the cache with the key. The value must be supported by the coder
‘s dump
and load
methods.
Returns true
if the write succeeded, nil
if there was an error talking to the cache backend, or false
if the write failed for another reason.
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 to1.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.
# File activesupport/lib/active_support/cache.rb, line 660 def write(name, value, options = nil) options = merged_options(options) key = normalize_key(name, options) instrument(:write, key, options) do entry = Entry.new(value, **options.merge(version: normalize_version(name, options))) write_entry(key, entry, **options) end end
write_multi(hash, options = nil) Link
Cache
Storage API to write multiple values at once.
# File activesupport/lib/active_support/cache.rb, line 550 def write_multi(hash, options = nil) return hash if hash.empty? options = merged_options(options) instrument_multi :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
Instance Private methods
key_matcher(pattern, options) Link
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 activesupport/lib/active_support/cache.rb, line 777 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