Class: ActiveSupport::Cache::Store
- Defined in:
- lib/active_support/cache.rb
Overview
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.
Direct Known Subclasses
FileStore, MemCacheStore, MemoryStore, NullStore, ActiveSupport::Cache::Strategy::LocalCache::LocalStore
Instance Attribute Summary collapse
-
#options ⇒ Object
readonly
Returns the value of attribute options.
-
#silence ⇒ Object
(also: #silence?)
readonly
Returns the value of attribute silence.
Class Method Summary collapse
- .instrument ⇒ Object
-
.instrument=(boolean) ⇒ Object
Set to true if cache stores should be instrumented.
Instance Method Summary collapse
-
#cleanup(options = nil) ⇒ Object
Cleanup the cache by removing expired entries.
-
#clear(options = nil) ⇒ Object
Clear the entire cache.
-
#decrement(name, amount = 1, options = nil) ⇒ Object
Increment an integer value in the cache.
-
#delete(name, options = nil) ⇒ Object
Deletes an entry in the cache.
-
#delete_matched(matcher, options = nil) ⇒ Object
Delete all entries with keys matching the pattern.
-
#exist?(name, options = nil) ⇒ Boolean
Return true if the cache contains an entry for the given key.
-
#fetch(name, options = nil) ⇒ Object
Fetches data from the cache, using the given key.
-
#increment(name, amount = 1, options = nil) ⇒ Object
Increment an integer value in the cache.
-
#initialize(options = nil) ⇒ Store
constructor
Create a new cache.
-
#mute ⇒ Object
Silence the logger within a block.
-
#read(name, options = nil) ⇒ Object
Fetches data from the cache, using the given key.
-
#read_multi(*names) ⇒ Object
Read multiple values at once from the cache.
-
#silence! ⇒ Object
Silence the logger.
-
#write(name, value, options = nil) ⇒ Object
Writes the value to the cache, with the key.
Constructor Details
#initialize(options = nil) ⇒ Store
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.
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# File 'lib/active_support/cache.rb', line 152 def initialize( = nil) @options = ? .dup : {} end |
Instance Attribute Details
#options ⇒ Object (readonly)
Returns the value of attribute options.
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# File 'lib/active_support/cache.rb', line 147 def @options end |
#silence ⇒ Object (readonly) Also known as: silence?
Returns the value of attribute silence.
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# File 'lib/active_support/cache.rb', line 147 def silence @silence end |
Class Method Details
.instrument ⇒ Object
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# File 'lib/active_support/cache.rb', line 175 def self.instrument Thread.current[:instrument_cache_store] || false end |
.instrument=(boolean) ⇒ Object
Set to true if cache stores should be instrumented. Default is false.
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# File 'lib/active_support/cache.rb', line 171 def self.instrument=(boolean) Thread.current[:instrument_cache_store] = boolean end |
Instance Method Details
#cleanup(options = nil) ⇒ Object
Cleanup the cache by removing expired entries.
Options are passed to the underlying cache implementation.
All implementations may not support this method.
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# File 'lib/active_support/cache.rb', line 425 def cleanup( = nil) raise NotImplementedError.new("#{self.class.name} does not support cleanup") end |
#clear(options = nil) ⇒ Object
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.
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# File 'lib/active_support/cache.rb', line 435 def clear( = nil) raise NotImplementedError.new("#{self.class.name} does not support clear") end |
#decrement(name, amount = 1, options = nil) ⇒ Object
Increment an integer value in the cache.
Options are passed to the underlying cache implementation.
All implementations may not support this method.
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# File 'lib/active_support/cache.rb', line 416 def decrement(name, amount = 1, = nil) raise NotImplementedError.new("#{self.class.name} does not support decrement") end |
#delete(name, options = nil) ⇒ Object
Deletes an entry in the cache. Returns true
if an entry is deleted.
Options are passed to the underlying cache implementation.
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# File 'lib/active_support/cache.rb', line 371 def delete(name, = nil) = () instrument(:delete, name) do |payload| delete_entry(namespaced_key(name, ), ) end end |
#delete_matched(matcher, options = nil) ⇒ Object
Delete all entries with keys matching the pattern.
Options are passed to the underlying cache implementation.
All implementations may not support this method.
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# File 'lib/active_support/cache.rb', line 398 def delete_matched(matcher, = nil) raise NotImplementedError.new("#{self.class.name} does not support delete_matched") end |
#exist?(name, options = nil) ⇒ Boolean
Return true if the cache contains an entry for the given key.
Options are passed to the underlying cache implementation.
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# File 'lib/active_support/cache.rb', line 381 def exist?(name, = nil) = () instrument(:exist?, name) do |payload| entry = read_entry(namespaced_key(name, ), ) if entry && !entry.expired? true else false end end end |
#fetch(name, options = nil) ⇒ Object
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"
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# File 'lib/active_support/cache.rb', line 271 def fetch(name, = nil) if block_given? = () key = namespaced_key(name, ) unless [:force] entry = instrument(:read, name, ) do |payload| payload[:super_operation] = :fetch if payload read_entry(key, ) end end if entry && entry.expired? race_ttl = [: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, ) end entry = nil end if entry instrument(:fetch_hit, name, ) { |payload| } entry.value else result = instrument(:generate, name, ) do |payload| yield end write(name, result, ) result end else read(name, ) end end |
#increment(name, amount = 1, options = nil) ⇒ Object
Increment an integer value in the cache.
Options are passed to the underlying cache implementation.
All implementations may not support this method.
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# File 'lib/active_support/cache.rb', line 407 def increment(name, amount = 1, = nil) raise NotImplementedError.new("#{self.class.name} does not support increment") end |
#mute ⇒ Object
Silence the logger within a block.
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# File 'lib/active_support/cache.rb', line 163 def mute previous_silence, @silence = defined?(@silence) && @silence, true yield ensure @silence = previous_silence end |
#read(name, options = nil) ⇒ Object
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.
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# File 'lib/active_support/cache.rb', line 312 def read(name, = nil) = () key = namespaced_key(name, ) instrument(:read, name, ) do |payload| entry = read_entry(key, ) if entry if entry.expired? delete_entry(key, ) 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) ⇒ Object
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.
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# File 'lib/active_support/cache.rb', line 339 def read_multi(*names) = names. = () results = {} names.each do |name| key = namespaced_key(name, ) entry = read_entry(key, ) if entry if entry.expired? delete_entry(key, ) else results[name] = entry.value end end end results end |
#silence! ⇒ Object
Silence the logger.
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# File 'lib/active_support/cache.rb', line 157 def silence! @silence = true self end |
#write(name, value, options = nil) ⇒ Object
Writes the value to the cache, with the key.
Options are passed to the underlying cache implementation.
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# File 'lib/active_support/cache.rb', line 360 def write(name, value, = nil) = () instrument(:write, name, ) do |payload| entry = Entry.new(value, ) write_entry(namespaced_key(name, ), entry, ) end end |