Redis cache store.

Deployment note: Take care to use a *dedicated Redis cache* rather than pointing this at your existing Redis server. It 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 end
 
DEFAULT_REDIS_OPTIONS = { connect_timeout: 20, read_timeout: 1, write_timeout: 1, reconnect_attempts: 0, }
 
MAX_KEY_BYTESIZE = 1024
 

Keys are truncated with their own SHA2 digest if they exceed 1kB

Attributes

[R] max_key_bytesize
[R] redis_options

Class Public methods

new(namespace: nil, compress: true, compress_threshold: 1.kilobyte, expires_in: nil, race_condition_ttl: nil, error_handler: DEFAULT_ERROR_HANDLER, **redis_options)

Creates a new Redis cache store.

Handles three options: block provided to instantiate, single URL provided, and multiple URLs provided.

:redis Proc   -> options[:redis].call
: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: <tt>namespace: 'myapp-cache'<tt>.

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.

# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 166
def initialize(namespace: nil, compress: true, compress_threshold: 1.kilobyte, expires_in: nil, race_condition_ttl: nil, error_handler: DEFAULT_ERROR_HANDLER, **redis_options)
  @redis_options = redis_options

  @max_key_bytesize = MAX_KEY_BYTESIZE
  @error_handler = error_handler

  super namespace: namespace,
    compress: compress, compress_threshold: compress_threshold,
    expires_in: expires_in, race_condition_ttl: race_condition_ttl
end

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.

# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 279
def cleanup(options = nil)
  super
end

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.

# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 287
def clear(options = nil)
  failsafe :clear do
    if namespace = merged_options(options)[:namespace]
      delete_matched "*", namespace: namespace
    else
      redis.with { |c| c.flushdb }
    end
  end
end

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

Cache Store API implementation.

Decrement a cached value. This method uses the Redis decr atomic operator and can only be used on values written with the :raw option. Calling it on a value not stored with :raw will initialize that value to zero.

Failsafe: Raises errors.

# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 267
def decrement(name, amount = 1, options = nil)
  instrument :decrement, name, amount: amount do
    failsafe :decrement do
      redis.with { |c| c.decrby normalize_key(name, options), amount }
    end
  end
end

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.

# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 226
def delete_matched(matcher, options = nil)
  instrument :delete_matched, matcher do
    unless String === matcher
      raise ArgumentError, "Only Redis glob strings are supported: #{matcher.inspect}"
    end
    redis.with do |c|
      pattern = namespace_key(matcher, options)
      cursor = "0"
      # Fetch keys in batches using SCAN to avoid blocking the Redis server.
      begin
        cursor, keys = c.scan(cursor, match: pattern, count: SCAN_BATCH_SIZE)
        c.del(*keys) unless keys.empty?
      end until cursor == "0"
    end
  end
end

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

Cache Store API implementation.

Increment a cached value. This method uses the Redis incr atomic operator and can only be used on values written with the :raw option. Calling it on a value not stored with :raw will initialize that value to zero.

Failsafe: Raises errors.

# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 251
def increment(name, amount = 1, options = nil)
  instrument :increment, name, amount: amount do
    failsafe :increment do
      redis.with { |c| c.incrby normalize_key(name, options), amount }
    end
  end
end

inspect()

# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 190
def inspect
  instance = @redis || @redis_options
  "<##{self.class} options=#{options.inspect} redis=#{instance.inspect}>"
end

read_multi(*names)

Cache Store API implementation.

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

# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 199
def read_multi(*names)
  if mget_capable?
    instrument(:read_multi, names, options) do |payload|
      read_multi_mget(*names).tap do |results|
        payload[:hits] = results.keys
      end
    end
  else
    super
  end
end

redis()

# File activesupport/lib/active_support/cache/redis_cache_store.rb, line 177
def redis
  @redis ||= begin
    pool_options = self.class.send(:retrieve_pool_options, redis_options)

    if pool_options.any?
      self.class.send(:ensure_connection_pool_added!)
      ::ConnectionPool.new(pool_options) { self.class.build_redis(**redis_options) }
    else
      self.class.build_redis(**redis_options)
    end
  end
end