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.
- C
- D
- E
- F
- I
- K
- M
- N
- R
- S
- W
[R] | options | |
[R] | silence | |
[R] | silence? |
Set to true if cache stores should be instrumented. Default is false.
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.
Cleanup the cache by removing expired entries.
Options are passed to the underlying cache implementation.
All implementations may not support this method.
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.
Increment an integer value in the cache.
Options are passed to the underlying cache implementation.
All implementations may not support this method.
Deletes an entry in the cache. Returns true
if an entry is
deleted.
Options are passed to the underlying cache implementation.
Delete all entries with keys matching the pattern.
Options are passed to the underlying cache implementation.
All implementations may not support this method.
Return 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 381 def exist?(name, options = nil) options = merged_options(options) instrument(:exist?, name) do |payload| entry = read_entry(namespaced_key(name, options), options) if entry && !entry.expired? true else false end 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 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"
# File activesupport/lib/active_support/cache.rb, line 271 def fetch(name, options = nil) if block_given? options = merged_options(options) key = namespaced_key(name, options) unless options[:force] entry = instrument(:read, name, options) do |payload| payload[:super_operation] = :fetch if payload read_entry(key, options) end end if entry && entry.expired? race_ttl = options[:race_condition_ttl].to_f if race_ttl and Time.now.to_f - entry.expires_at <= race_ttl 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 if entry instrument(:fetch_hit, name, options) { |payload| } entry.value else result = instrument(:generate, name, options) do |payload| yield end write(name, result, options) result end else read(name, options) end end
Increment an integer value in the cache.
Options are passed to the underlying cache implementation.
All implementations may not support this method.
Silence the logger within a block.
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 activesupport/lib/active_support/cache.rb, line 312 def read(name, options = nil) options = merged_options(options) key = namespaced_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
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.
# File activesupport/lib/active_support/cache.rb, line 339 def read_multi(*names) options = names.extract_options! options = merged_options(options) results = {} names.each do |name| key = namespaced_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
Silence the logger.
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 360 def write(name, value, options = nil) options = merged_options(options) instrument(:write, name, options) do |payload| entry = Entry.new(value, options) write_entry(namespaced_key(name, options), entry, options) end end
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.
# File activesupport/lib/active_support/cache.rb, line 443 def key_matcher(pattern, options) 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