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
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Supports vanilla Redis, hiredis, and Redis::Distributed.
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Supports Memcached-like sharding across Redises with Redis::Distributed.
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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.
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read_multi
andwrite_multi
support for Redis mget/mset. Use Redis::Distributed 4.0.1+ for distributed mget support. -
delete_matched
support for Redis KEYS globs.
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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 |
[R] | max_key_bytesize | |
[R] | 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
Clear the entire cache on all Redis servers. Safe to use on shared servers if the cache is namespaced.
Failsafe: Raises errors.
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
# 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