Redis Cache Store

Deployment note: Take care to use a dedicated Redis cache rather than pointing this at a persistent Redis server (for example, one used as an Active Job queue). Redis won’t cope well with mixed usage patterns and it won’t expire cache entries by default.

Redis cache server setup guide: redis.io/topics/lru-cache

  • Supports vanilla Redis, hiredis, and Redis::Distributed.

  • Supports Memcached-like sharding across Redises with Redis::Distributed.

  • Fault tolerant. If the Redis server is unavailable, no exceptions are raised. Cache fetches are all misses and writes are dropped.

  • Local cache. Hot in-memory primary cache within block/middleware scope.

  • read_multi and write_multi support for Redis mget/mset. Use Redis::Distributed 4.0.1+ for distributed mget support.

  • delete_matched support for Redis KEYS globs.

Methods

Constants

DEFAULT_ERROR_HANDLER = -> (method:, returning:, exception:) do if logger logger.error { "RedisCacheStore: #{method} failed, returned #{returning.inspect}: #{exception.class}: #{exception.message}" } end ActiveSupport.error_reporter&.report( exception, severity: :warning, source: "redis_cache_store.active_support", ) end
DEFAULT_REDIS_OPTIONS = { connect_timeout: 1, read_timeout: 1, write_timeout: 1, }
MAX_KEY_BYTESIZE = 1024
 

Keys are truncated with the Active Support digest if they exceed 1kB

Attributes

[R] max_key_bytesize
[R] redis

Class Public methods

new(error_handler: DEFAULT_ERROR_HANDLER, **redis_options)

Creates a new Redis cache store.

There are four ways to provide the Redis client used by the cache: the :redis param can be a Redis instance or a block that returns a Redis instance, or the :url param can be a string or an array of strings which will be used to create a Redis instance or a Redis::Distributed instance.

Option  Class       Result
:redis  Proc    ->  options[:redis].call
:redis  Object  ->  options[:redis]
:url    String  ->  Redis.new(url: …)
:url    Array   ->  Redis::Distributed.new([{ url: … }, { url: … }, …])

No namespace is set by default. Provide one if the Redis cache server is shared with other apps: namespace: 'myapp-cache'.

Compression is enabled by default with a 1kB threshold, so cached values larger than 1kB are automatically compressed. Disable by passing compress: false or change the threshold by passing compress_threshold: 4.kilobytes.

No expiry is set on cache entries by default. Redis is expected to be configured with an eviction policy that automatically deletes least-recently or -frequently used keys when it reaches max memory. See redis.io/topics/lru-cache for cache server setup.

Race condition TTL is not set by default. This can be used to avoid “thundering herd” cache writes when hot cache entries are expired. See ActiveSupport::Cache::Store#fetch for more.

Setting skip_nil: true will not cache nil results:

cache.fetch('foo') { nil }
cache.fetch('bar', skip_nil: true) { nil }
cache.exist?('foo') # => true
cache.exist?('bar') # => false
📝 Source code 
# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 149
      def initialize(error_handler: DEFAULT_ERROR_HANDLER, **redis_options)
        universal_options = redis_options.extract!(*UNIVERSAL_OPTIONS)

        if pool_options = self.class.send(:retrieve_pool_options, redis_options)
          @redis = ::ConnectionPool.new(pool_options) { self.class.build_redis(**redis_options) }
        else
          @redis = self.class.build_redis(**redis_options)
        end

        @max_key_bytesize = MAX_KEY_BYTESIZE
        @error_handler = error_handler

        super(universal_options)
      end
🔎 See on GitHub

supports_cache_versioning?()

Advertise cache versioning support.

📝 Source code 
# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 63
      def self.supports_cache_versioning?
        true
      end
🔎 See on GitHub

Instance Public methods

cleanup(options = nil)

Cache Store API implementation.

Removes expired entries. Handled natively by Redis least-recently-/ least-frequently-used expiry, so manual cleanup is not supported.

📝 Source code 
# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 282
      def cleanup(options = nil)
        super
      end
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clear(options = nil)

Clear the entire cache on all Redis servers. Safe to use on shared servers if the cache is namespaced.

Failsafe: Raises errors.

📝 Source code 
# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 290
      def clear(options = nil)
        failsafe :clear do
          if namespace = merged_options(options)[:namespace]
            delete_matched "*", namespace: namespace
          else
            redis.then { |c| c.flushdb }
          end
        end
      end
🔎 See on GitHub

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

Decrement a cached integer value using the Redis decrby atomic operator. Returns the updated value.

If the key is unset or has expired, it will be set to -amount:

cache.decrement("foo") # => -1

To set a specific value, call write passing raw: true:

cache.write("baz", 5, raw: true)
cache.decrement("baz") # => 4

Decrementing a non-numeric value, or a value written without raw: true, will fail and return nil.

Failsafe: Raises errors.

📝 Source code 
# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 267
      def decrement(name, amount = 1, options = nil)
        options = merged_options(options)
        key = normalize_key(name, options)

        instrument :decrement, key, amount: amount do
          failsafe :decrement do
            change_counter(key, -amount, options)
          end
        end
      end
🔎 See on GitHub

delete_matched(matcher, options = nil)

Cache Store API implementation.

Supports Redis KEYS glob patterns:

h?llo matches hello, hallo and hxllo
h*llo matches hllo and heeeello
h[ae]llo matches hello and hallo, but not hillo
h[^e]llo matches hallo, hbllo, ... but not hello
h[a-b]llo matches hallo and hbllo

Use \ to escape special characters if you want to match them verbatim.

See redis.io/commands/KEYS for more.

Failsafe: Raises errors.

📝 Source code 
# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 201
      def delete_matched(matcher, options = nil)
        unless String === matcher
          raise ArgumentError, "Only Redis glob strings are supported: #{matcher.inspect}"
        end
        pattern = namespace_key(matcher, options)

        instrument :delete_matched, pattern do
          redis.then do |c|
            cursor = "0"
            # Fetch keys in batches using SCAN to avoid blocking the Redis server.
            nodes = c.respond_to?(:nodes) ? c.nodes : [c]

            nodes.each do |node|
              begin
                cursor, keys = node.scan(cursor, match: pattern, count: SCAN_BATCH_SIZE)
                node.del(*keys) unless keys.empty?
              end until cursor == "0"
            end
          end
        end
      end
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increment(name, amount = 1, options = nil)

Increment a cached integer value using the Redis incrby atomic operator. Returns the updated value.

If the key is unset or has expired, it will be set to amount:

cache.increment("foo") # => 1
cache.increment("bar", 100) # => 100

To set a specific value, call write passing raw: true:

cache.write("baz", 5, raw: true)
cache.increment("baz") # => 6

Incrementing a non-numeric value, or a value written without raw: true, will fail and return nil.

Failsafe: Raises errors.

📝 Source code 
# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 240
      def increment(name, amount = 1, options = nil)
        options = merged_options(options)
        key = normalize_key(name, options)

        instrument :increment, key, amount: amount do
          failsafe :increment do
            change_counter(key, amount, options)
          end
        end
      end
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inspect()

📝 Source code 
# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 164
      def inspect
        "#<#{self.class} options=#{options.inspect} redis=#{redis.inspect}>"
      end
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read_multi(*names)

Cache Store API implementation.

Read multiple values at once. Returns a hash of requested keys -> fetched values.

📝 Source code 
# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 172
      def read_multi(*names)
        return {} if names.empty?

        options = names.extract_options!
        options = merged_options(options)
        keys    = names.map { |name| normalize_key(name, options) }

        instrument_multi(:read_multi, keys, options) do |payload|
          read_multi_entries(names, **options).tap do |results|
            payload[:hits] = results.keys.map { |name| normalize_key(name, options) }
          end
        end
      end
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stats()

Get info from redis servers.

📝 Source code 
# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 301
      def stats
        redis.then { |c| c.info }
      end
🔎 See on GitHub