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
Cached data larger than 1kB are compressed by default. To turn off compression, pass compress: false
to the initializer or to individual fetch
or write
method calls. The 1kB compression threshold is configurable with the :compress_threshold
option, specified in bytes.
- C
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Constants
DEFAULT_CODER | = | Marshal |
Attributes
[R] | options | |
[R] | silence | |
[R] | silence? |
Class Public methods
new(options = nil) Link
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.
Instance Public methods
cleanup(options = nil) Link
Cleanups 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.
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.
Options are passed to the underlying cache implementation.
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 506 def exist?(name, options = nil) options = merged_options(options) instrument(:exist?, name) do |payload| entry = read_entry(normalize_key(name, options), **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"
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 skip_nil: true
will not cache nil result:
cache.fetch('foo') { nil }
cache.fetch('bar', skip_nil: true) { nil }
cache.exist?('foo') # => true
cache.exist?('bar') # => false
Setting compress: false
disables compression of the cache entry.
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 :version
verifies the cache stored under name
is of the same version. nil is returned on mismatches despite contents. This feature is used to support recyclable cache keys.
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 activesupport/lib/active_support/cache.rb, line 326 def fetch(name, options = nil, &block) 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, event: payload) unless options[:force] entry = handle_expired_entry(cached_entry, key, options) entry = nil if entry && entry.mismatched?(normalize_version(name, 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, &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" }
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 446 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) instrument :read_multi, names, options do |payload| reads = read_multi_entries(names, **options) writes = {} ordered = names.index_with do |name| reads.fetch(name) { writes[name] = yield(name) } end payload[:hits] = reads.keys payload[:super_operation] = :fetch_multi write_multi(writes, options) ordered end 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 are passed to the underlying cache implementation.
# File activesupport/lib/active_support/cache.rb, line 361 def read(name, options = nil) options = merged_options(options) key = normalize_key(name, options) version = normalize_version(name, options) instrument(:read, name, 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 entry.value 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 394 def read_multi(*names) options = names.extract_options! options = merged_options(options) instrument :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.
Options are passed to the underlying cache implementation.
# File activesupport/lib/active_support/cache.rb, line 471 def write(name, value, options = nil) options = merged_options(options) instrument(:write, name, options) do entry = Entry.new(value, **options.merge(version: normalize_version(name, options))) write_entry(normalize_key(name, options), 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 406 def write_multi(hash, options = nil) options = merged_options(options) instrument :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 566 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