Class: ActiveSupport::Cache::Store

Alias for #silence.

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.

Decrements an integer value in the cache.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

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

Options are passed to the underlying cache implementation.

Deletes all entries with keys matching the pattern.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

Deletes multiple entries in the cache. Returns the number of deleted entries.

Options are passed to the underlying cache implementation.

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

Options are passed to the underlying cache implementation.

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 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 #write.

• 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 # => "original 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 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

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

Increments an integer value in the cache.

Options are passed to the underlying cache implementation.

Some implementations may not support this method.

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.

Silences the logger within a block.

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.

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.

Silences the logger.

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 to 1.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.

::ActiveSupport::Cache Storage API to write multiple values at once.