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 = lambda { @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.

Methods

C

cleanup,
clear

D

decrement,
delete,
delete_matched

E

exist?

F

fetch

I

increment,
instrument,
instrument=

K

key_matcher

M

mute

N

new

R

read,
read_multi

S

silence!

W

write

Attributes

[R]	silence
[R]	options

Class Public methods

instrument()

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 175
175:       def self.instrument
176:         Thread.current[:instrument_cache_store] || false
177:       end

instrument=(boolean)

Set to true if cache stores should be instrumented. Default is false.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 171
171:       def self.instrument=(boolean)
172:         Thread.current[:instrument_cache_store] = boolean
173:       end

new(options = nil)

Create 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.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 152
152:       def initialize(options = nil)
153:         @options = options ? options.dup : {}
154:       end

Instance Public methods

cleanup(options = nil)

Cleanup the cache by removing expired entries.

Options are passed to the underlying cache implementation.

All implementations may not support this method.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 425
425:       def cleanup(options = nil)
426:         raise NotImplementedError.new("#{self.class.name} does not support cleanup")
427:       end

clear(options = nil)

Clear the entire cache. Be careful with this method since it could affect other processes if shared cache is being used.

Options are passed to the underlying cache implementation.

All implementations may not support this method.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 435
435:       def clear(options = nil)
436:         raise NotImplementedError.new("#{self.class.name} does not support clear")
437:       end

decrement(name, amount = 1, options = nil)

Increment an integer value in the cache.

Options are passed to the underlying cache implementation.

All implementations may not support this method.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 416
416:       def decrement(name, amount = 1, options = nil)
417:         raise NotImplementedError.new("#{self.class.name} does not support decrement")
418:       end

delete(name, options = nil)

Deletes an entry in the cache. Returns true if an entry is deleted.

Options are passed to the underlying cache implementation.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 371
371:       def delete(name, options = nil)
372:         options = merged_options(options)
373:         instrument(:delete, name) do |payload|
374:           delete_entry(namespaced_key(name, options), options)
375:         end
376:       end

delete_matched(matcher, options = nil)

Delete all entries with keys matching the pattern.

Options are passed to the underlying cache implementation.

All implementations may not support this method.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 398
398:       def delete_matched(matcher, options = nil)
399:         raise NotImplementedError.new("#{self.class.name} does not support delete_matched")
400:       end

exist?(name, options = nil)

Return true if the cache contains an entry for the given key.

Options are passed to the underlying cache implementation.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 381
381:       def exist?(name, options = nil)
382:         options = merged_options(options)
383:         instrument(:exist?, name) do |payload|
384:           entry = read_entry(namespaced_key(name, options), options)
385:           if entry && !entry.expired?
386:             true
387:           else
388:             false
389:           end
390:         end
391:       end

fetch(name, options = nil)

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 run 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 will force a cache miss:

  cache.write("today", "Monday")
  cache.fetch("today", :force => true)  # => nil

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 seven 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 big 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 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) do
      sleep 1
      "new value 1"
    end
  end

  Thread.new do
    val_2 = cache.fetch("foo", :race_condition_ttl => 10) do
      "new value 2"
    end
  end

  # val_1 => "new value 1"
  # val_2 => "original value"
  # sleep 10 # First thread extend the life of cache by another 10 seconds
  # cache.fetch("foo") => "new value 1"

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"

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 271
271:       def fetch(name, options = nil)
272:         if block_given?
273:           options = merged_options(options)
274:           key = namespaced_key(name, options)
275:           unless options[:force]
276:             entry = instrument(:read, name, options) do |payload|
277:               payload[:super_operation] = :fetch if payload
278:               read_entry(key, options)
279:             end
280:           end
281:           if entry && entry.expired?
282:             race_ttl = options[:race_condition_ttl].to_f
283:             if race_ttl and Time.now.to_f - entry.expires_at <= race_ttl
284:               entry.expires_at = Time.now + race_ttl
285:               write_entry(key, entry, :expires_in => race_ttl * 2)
286:             else
287:               delete_entry(key, options)
288:             end
289:             entry = nil
290:           end
291: 
292:           if entry
293:             instrument(:fetch_hit, name, options) { |payload| }
294:             entry.value
295:           else
296:             result = instrument(:generate, name, options) do |payload|
297:               yield
298:             end
299:             write(name, result, options)
300:             result
301:           end
302:         else
303:           read(name, options)
304:         end
305:       end

increment(name, amount = 1, options = nil)

Increment an integer value in the cache.

Options are passed to the underlying cache implementation.

All implementations may not support this method.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 407
407:       def increment(name, amount = 1, options = nil)
408:         raise NotImplementedError.new("#{self.class.name} does not support increment")
409:       end

mute()

Silence the logger within a block.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 163
163:       def mute
164:         previous_silence, @silence = defined?(@silence) && @silence, true
165:         yield
166:       ensure
167:         @silence = previous_silence
168:       end

read(name, options = nil)

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.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 312
312:       def read(name, options = nil)
313:         options = merged_options(options)
314:         key = namespaced_key(name, options)
315:         instrument(:read, name, options) do |payload|
316:           entry = read_entry(key, options)
317:           if entry
318:             if entry.expired?
319:               delete_entry(key, options)
320:               payload[:hit] = false if payload
321:               nil
322:             else
323:               payload[:hit] = true if payload
324:               entry.value
325:             end
326:           else
327:             payload[:hit] = false if payload
328:             nil
329:           end
330:         end
331:       end

read_multi(*names)

Read 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.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 339
339:       def read_multi(*names)
340:         options = names.extract_options!
341:         options = merged_options(options)
342:         results = {}
343:         names.each do |name|
344:           key = namespaced_key(name, options)
345:           entry = read_entry(key, options)
346:           if entry
347:             if entry.expired?
348:               delete_entry(key, options)
349:             else
350:               results[name] = entry.value
351:             end
352:           end
353:         end
354:         results
355:       end

silence!()

Silence the logger.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 157
157:       def silence!
158:         @silence = true
159:         self
160:       end

write(name, value, options = nil)

Writes the value to the cache, with the key.

Options are passed to the underlying cache implementation.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 360
360:       def write(name, value, options = nil)
361:         options = merged_options(options)
362:         instrument(:write, name, options) do |payload|
363:           entry = Entry.new(value, options)
364:           write_entry(namespaced_key(name, options), entry, options)
365:         end
366:       end

Instance Protected methods

key_matcher(pattern, options)

Add 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.

Source: show | on GitHub

     # File activesupport/lib/active_support/cache.rb, line 443
443:         def key_matcher(pattern, options)
444:           prefix = options[:namespace].is_a?(Proc) ? options[:namespace].call : options[:namespace]
445:           if prefix
446:             source = pattern.source
447:             if source.start_with?('^')
448:               source = source[1, source.length]
449:             else
450:               source = ".*#{source[0, source.length]}"
451:             end
452:             Regexp.new("^#{Regexp.escape(prefix)}:#{source}", pattern.options)
453:           else
454:             pattern
455:           end
456:         end