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Diffstat (limited to 'guides/source/caching_with_rails.md')
| -rw-r--r-- | guides/source/caching_with_rails.md | 75 |
1 files changed, 50 insertions, 25 deletions
diff --git a/guides/source/caching_with_rails.md b/guides/source/caching_with_rails.md index 780e69c146..8aaa71c557 100644 --- a/guides/source/caching_with_rails.md +++ b/guides/source/caching_with_rails.md @@ -1,4 +1,4 @@ -**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON http://guides.rubyonrails.org.** +**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON https://guides.rubyonrails.org.** Caching with Rails: An Overview =============================== @@ -100,9 +100,9 @@ called key-based expiration. Cache fragments will also be expired when the view fragment changes (e.g., the HTML in the view changes). The string of characters at the end of the key is a -template tree digest. It is an MD5 hash computed based on the contents of the -view fragment you are caching. If you change the view fragment, the MD5 hash -will change, expiring the existing file. +template tree digest. It is a hash digest computed based on the contents of the +view fragment you are caching. If you change the view fragment, the digest will +change, expiring the existing file. TIP: Cache stores like Memcached will automatically delete old cache files. @@ -408,7 +408,7 @@ as well as development and test environments. New Rails projects are configured to use this implementation in development environment by default. NOTE: Since processes will not share cache data when using `:memory_store`, -it will not be possible to manually read, write or expire the cache via the Rails console. +it will not be possible to manually read, write, or expire the cache via the Rails console. ### ActiveSupport::Cache::FileStore @@ -446,26 +446,28 @@ config.cache_store = :mem_cache_store, "cache-1.example.com", "cache-2.example.c ### ActiveSupport::Cache::RedisCacheStore -The Redis cache store takes advantage of Redis support for least-recently-used -and least-frequently-used key eviction when it reaches max memory, allowing it -to behave much like a Memcached cache server. +The Redis cache store takes advantage of Redis support for automatic eviction +when it reaches max memory, allowing it to behave much like a Memcached cache server. Deployment note: Redis doesn't expire keys by default, so take care to use a dedicated Redis cache server. Don't fill up your persistent-Redis server with volatile cache data! Read the [Redis cache server setup guide](https://redis.io/topics/lru-cache) in detail. -For an all-cache Redis server, set `maxmemory-policy` to an `allkeys` policy. -Redis 4+ support least-frequently-used (`allkeys-lfu`) eviction, an excellent -default choice. Redis 3 and earlier should use `allkeys-lru` for -least-recently-used eviction. +For a cache-only Redis server, set `maxmemory-policy` to one of the variants of allkeys. +Redis 4+ supports least-frequently-used eviction (`allkeys-lfu`), an excellent +default choice. Redis 3 and earlier should use least-recently-used eviction (`allkeys-lru`). Set cache read and write timeouts relatively low. Regenerating a cached value is often faster than waiting more than a second to retrieve it. Both read and write timeouts default to 1 second, but may be set lower if your network is -consistently low latency. +consistently low-latency. -Cache reads and writes never raise exceptions. They just return `nil` instead, +By default, the cache store will not attempt to reconnect to Redis if the +connection fails during a request. If you experience frequent disconnects you +may wish to enable reconnect attempts. + +Cache reads and writes never raise exceptions; they just return `nil` instead, behaving as if there was nothing in the cache. To gauge whether your cache is hitting exceptions, you may provide an `error_handler` to report to an exception gathering service. It must accept three keyword arguments: `method`, @@ -473,22 +475,45 @@ the cache store method that was originally called; `returning`, the value that was returned to the user, typically `nil`; and `exception`, the exception that was rescued. -Putting it all together, a production Redis cache store may look something -like this: +To get started, add the redis gem to your Gemfile: + +```ruby +gem 'redis' +``` + +You can enable support for the faster [hiredis](https://github.com/redis/hiredis) +connection library by additionally adding its ruby wrapper to your Gemfile: + +```ruby +gem 'hiredis' +``` + +Redis cache store will automatically require & use hiredis if available. No further +configuration is needed. + +Finally, add the configuration in the relevant `config/environments/*.rb` file: + +```ruby +config.cache_store = :redis_cache_store, { url: ENV['REDIS_URL'] } +``` + +A more complex, production Redis cache store may look something like this: ```ruby -cache_servers = %w[ "redis://cache-01:6379/0", "redis://cache-02:6379/0", … ], -config.cache_store = :redis_cache_store, url: cache_servers, +cache_servers = %w(redis://cache-01:6379/0 redis://cache-02:6379/0) +config.cache_store = :redis_cache_store, { url: cache_servers, - connect_timeout: 30, # Defaults to 20 seconds - read_timeout: 0.2, # Defaults to 1 second - write_timeout: 0.2, # Defaults to 1 second + connect_timeout: 30, # Defaults to 20 seconds + read_timeout: 0.2, # Defaults to 1 second + write_timeout: 0.2, # Defaults to 1 second + reconnect_attempts: 1, # Defaults to 0 error_handler: -> (method:, returning:, exception:) { # Report errors to Sentry as warnings - Raven.capture_exception exception, level: 'warning", + Raven.capture_exception exception, level: 'warning', tags: { method: method, returning: returning } } +} ``` ### ActiveSupport::Cache::NullStore @@ -645,13 +670,13 @@ Caching in Development ---------------------- It's common to want to test the caching strategy of your application -in development mode. Rails provides the rake task `dev:cache` to +in development mode. Rails provides the rails command `dev:cache` to easily toggle caching on/off. ```bash -$ bin/rails dev:cache +$ rails dev:cache Development mode is now being cached. -$ bin/rails dev:cache +$ rails dev:cache Development mode is no longer being cached. ``` |