diff options
Diffstat (limited to 'activesupport/lib/active_support/cache.rb')
| -rw-r--r-- | activesupport/lib/active_support/cache.rb | 93 |
1 files changed, 45 insertions, 48 deletions
diff --git a/activesupport/lib/active_support/cache.rb b/activesupport/lib/active_support/cache.rb index 0efb1a9458..8e90de110a 100644 --- a/activesupport/lib/active_support/cache.rb +++ b/activesupport/lib/active_support/cache.rb @@ -127,13 +127,6 @@ module ActiveSupport # cache.namespace = lambda { @last_mod_time } # Set the namespace to a variable # @last_mod_time = Time.now # Invalidate the entire cache by changing namespace # - # All caches support auto expiring content after a specified number of seconds. - # To set the cache entry time to live, you can either specify +:expires_in+ as - # an option to the constructor to have it affect all entries or to the +fetch+ - # or +write+ methods for just one entry. - # - # cache = ActiveSupport::Cache::MemoryStore.new(:expire_in => 5.minutes) - # cache.write(key, value, :expire_in => 1.minute) # Set a lower value for one entry # # Caches can also store values in a compressed format to save space and reduce # time spent sending data. Since there is some overhead, values must be large @@ -173,7 +166,7 @@ module ActiveSupport @silence = previous_silence end - # Set to true if cache stores should be instrumented. By default is false. + # Set to true if cache stores should be instrumented. Default is false. def self.instrument=(boolean) Thread.current[:instrument_cache_store] = boolean end @@ -185,7 +178,7 @@ module ActiveSupport # 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 occurred), then + # If there is no such data in the cache (a cache miss occurred), # then nil will be returned. However, if a block has been passed, then # 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, @@ -209,23 +202,30 @@ module ActiveSupport # Setting <tt>:compress</tt> will store a large cache entry set by the call # in a compressed format. # - # Setting <tt>:expires_in</tt> will set an expiration time on the cache - # entry if it is set by call. # - # Setting <tt>:race_condition_ttl</tt> will invoke logic on entries set with - # an <tt>:expires_in</tt> option. If an entry is found in the cache that is - # expired and it has been expired for less than the number of seconds specified - # by this option and a block was passed to the method call, then the expiration - # future time of the entry in the cache will be updated to that many seconds - # in the and the block will be evaluated and written to the cache. + # Setting <tt>:expires_in</tt> 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 construction in which call all entries will be + # affected. Or it can be supplied to the +fetch+ or +write+ method for just one entry. + # + # cache = ActiveSupport::Cache::MemoryStore.new(:expire_in => 5.minutes) + # cache.write(key, value, :expire_in => 1.minute) # Set a lower value for one entry + # + # Setting <tt>:race_condition_ttl</tt> is very useful in situations where a cache entry + # is used very frequently unver 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 <tt>:race_condition_ttl</tt>. 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 <tt>:race_condition_ttl</tt> small. # - # This is very useful in situations where a cache entry is used very frequently - # under heavy load. The first process to find an expired cache entry will then - # become responsible for regenerating that entry while other processes continue - # to use the slightly out of date entry. This can prevent race conditions where - # too many processes are trying to regenerate the entry all at once. If the - # process regenerating the entry errors out, the entry will be regenerated - # after the specified number of seconds. + # 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 + # <tt>:race_condition_ttl</tt> does not play any role. # # # Set all values to expire after one minute. # cache = ActiveSupport::Cache::MemoryCache.new(:expires_in => 1.minute) @@ -250,6 +250,7 @@ module ActiveSupport # # # 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. @@ -351,11 +352,9 @@ module ActiveSupport results end - # Writes the given value to the cache, with the given key. + # Writes the value to the cache, with the key. # - # You may also specify additional options via the +options+ argument. - # The specific cache store implementation will decide what to do with - # +options+. + # Options are passed to the underlying cache implementation. def write(name, value, options = nil) options = merged_options(options) instrument(:write, name, options) do |payload| @@ -364,7 +363,7 @@ module ActiveSupport end end - # Delete an entry in the cache. Returns +true+ if there was an entry to delete. + # Deletes an entry in the cache. Returns +true+ if an entry is deleted. # # Options are passed to the underlying cache implementation. def delete(name, options = nil) @@ -374,7 +373,7 @@ module ActiveSupport end end - # Return true if the cache contains an entry with this name. + # Return true if the cache contains an entry for the given key. # # Options are passed to the underlying cache implementation. def exist?(name, options = nil) @@ -389,11 +388,11 @@ module ActiveSupport end end - # Delete all entries whose keys match a pattern. + # Delete all entries with keys matching the pattern. # # Options are passed to the underlying cache implementation. # - # Not all implementations may support +delete_matched+. + # All implementations may not support this method. def delete_matched(matcher, options = nil) raise NotImplementedError.new("#{self.class.name} does not support delete_matched") end @@ -402,7 +401,7 @@ module ActiveSupport # # Options are passed to the underlying cache implementation. # - # Not all implementations may support +delete_matched+. + # All implementations may not support this method. def increment(name, amount = 1, options = nil) raise NotImplementedError.new("#{self.class.name} does not support increment") end @@ -411,28 +410,26 @@ module ActiveSupport # # Options are passed to the underlying cache implementation. # - # Not all implementations may support +delete_matched+. + # All implementations may not support this method. def decrement(name, amount = 1, options = nil) raise NotImplementedError.new("#{self.class.name} does not support decrement") end - # Cleanup the cache by removing expired entries. Not all cache implementations may - # support this method. + # Cleanup the cache by removing expired entries. # # Options are passed to the underlying cache implementation. # - # Not all implementations may support +delete_matched+. + # All implementations may not support this method. def cleanup(options = nil) raise NotImplementedError.new("#{self.class.name} does not support cleanup") end - # Clear the entire cache. Not all cache implementations may support this method. - # You should be careful with this method since it could affect other processes - # if you are using a shared cache. + # 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. # - # Not all implementations may support +delete_matched+. + # All implementations may not support this method. def clear(options = nil) raise NotImplementedError.new("#{self.class.name} does not support clear") end @@ -481,9 +478,9 @@ module ActiveSupport end end - # Expand a key to be a consistent string value. If the object responds to +cache_key+, - # it will be called. Otherwise, the to_param method will be called. If the key is a - # Hash, the keys will be sorted alphabetically. + # Expand key to be a consistent string value. Invoke +cache_key+ if + # object responds to +cache_key+. Otherwise, to_param method will be + # called. If the key is a Hash, then keys will be sorted alphabetically. def expanded_key(key) # :nodoc: if key.respond_to?(:cache_key) key = key.cache_key.to_s @@ -500,7 +497,7 @@ module ActiveSupport end end - # Prefix a key with the namespace. The two values will be delimited with a colon. + # Prefix a key with the namespace. Namespace and key will be delimited with a colon. def namespaced_key(key, options) key = expanded_key(key) namespace = options[:namespace] if options @@ -597,7 +594,7 @@ module ActiveSupport end end - # Set a new time to live on the entry so it expires at the given time. + # Set a new time when the entry will expire. def expires_at=(time) if time @expires_in = time.to_f - @created_at @@ -606,12 +603,12 @@ module ActiveSupport end end - # Seconds since the epoch when the cache entry will expire. + # Seconds since the epoch when the entry will expire. def expires_at @expires_in ? @created_at + @expires_in : nil end - # Get the size of the cached value. This could be less than value.size + # Returns the size of the cached value. This could be less than value.size # if the data is compressed. def size if @value.nil? |