Built-in Redis cache store #31134

jeremy · 2017-11-12T23:58:35Z

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 treated as misses and writes are dropped.
Local cache. Hot in-memory primary cache within block/middleware scope.
read_/write_multi support for Redis mget/mset. Use Redis::Distributed 4.0.1+ for distributed mget support.
delete_matched support for Redis KEYS globs.

      # Defaults to `redis://localhost:6379/0`
      config.cache_store = :redis_cache_store

      # Supports all common cache store options (:namespace, :compress,
      # :compress_threshold, :expires_in, :race_condition_tool) and all
      # Redis options.
      cache_password = Rails.application.secrets.redis_cache_password
      config.cache_store = :redis_cache_store, driver: :hiredis,
        namespace: 'myapp-cache', compress: true, timeout: 1,
        url: "redis://:#{cache_password}@myapp-cache-1:6379/0"

      # Supports Redis::Distributed with multiple hosts
      config.cache_store = :redis_cache_store, driver: :hiredis
        namespace: 'myapp-cache', compress: true,
        url: %w[
          redis://myapp-cache-1:6379/0
          redis://myapp-cache-1:6380/0
          redis://myapp-cache-2:6379/0
          redis://myapp-cache-2:6380/0
          redis://myapp-cache-3:6379/0
          redis://myapp-cache-3:6380/0
        ]

      # Or pass a builder block
      config.cache_store = :redis_cache_store,
        namespace: 'myapp-cache', compress: true,
        redis: -> { Redis.new … }

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: https://redis.io/topics/lru-cache

jeremy · 2017-11-13T04:36:43Z

.travis.yml

@@ -41,7 +42,7 @@ before_script:
  # Decodes to e.g. `export VARIABLE=VALUE`
  - $(base64 --decode <<< "ZXhwb3J0IFNBVUNFX0FDQ0VTU19LRVk9YTAzNTM0M2YtZTkyMi00MGIzLWFhM2MtMDZiM2VhNjM1YzQ4")
  - $(base64 --decode <<< "ZXhwb3J0IFNBVUNFX1VTRVJOQU1FPXJ1YnlvbnJhaWxz")
-  - redis-server --bind 127.0.0.1 --port 6379 --requirepass 'password' --daemonize yes
+  - redis-server --bind 127.0.0.1 --port 6380 --requirepass 'password' --daemonize yes


Separate Redis for Action Cable tests which specifically want to work against a non-default config.

Use the default redis-server service for Active Support cache store tests.

Maybe we should have the test suite spin this up & down directly? Having to set a password on my local redis to get the tests to pass was annoying, but making everyone manually run a second instance seems even worse.

Yeah. I'd rather change the Action Cable tests separately. The point of this was to demonstrate that AC would accept user credentials for Redis. A mocked test should be sufficient. Then we can use a default Redis config for all tests.

Done in #31136

jeremy · 2017-11-13T04:36:43Z

activesupport/lib/active_support/cache.rb

+            "#{namespace}:#{key}"
+          else
+            key
+          end
        end


Separated this method from normalize_key so they may be overridden and called independently by subclasses.

The Redis cache store hashes cache keys larger than 1kB and it namespaces deleted_matched globs, which aren't keys to be normalized.

This method was removed from public API in Rails 5.0. #22215 for context.

I'll call it namespace_key instead, matching verb tense with normalize_key. (It's a different method than the old namespaced_key which expanded, sanitized, namespaced, etc.)

jeremy · 2017-11-13T04:36:43Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+
+begin
+  require "redis"
+  require "redis/distributed"


Always require redis/distributed, even if we use a single Redis, so we can reference Redis::Distributed::CannotDistribute below.

jeremy · 2017-11-13T04:36:43Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+begin
+  require "redis/connection/hiredis"
+rescue LoadError
+end


Maybe it's dubious. Maybe it's good practice. Maybe it's …

jeremy · 2017-11-13T04:36:43Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+end
+
+require "digest/md5"
+require "active_support/core_ext/marshal"


For large-key truncation and for entry marshaling.

md5 can be problematic; while it is slower, I think we should probably just use sha2.

Agree. I used MD5 to match MemCacheStore. I'd like to flip them both.

Switched to SHA2. MemCacheStore can catch up later.

jeremy · 2017-11-13T04:36:43Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+          else
+            super
+          end
+        end


Same story here, assuming #mset-capable and falling back if not.

jeremy · 2017-11-13T04:36:43Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+          else
+            key
+          end
+        end


Worth hoisting this out too.

jeremy · 2017-11-13T04:36:43Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+
+        def failsafe(method, returning: nil)
+          yield
+        rescue ::Redis::BaseConnectionError => e


May need to expand the set of failsafe exceptions, and allow Rails users to do it.

jeremy · 2017-11-13T04:36:43Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+          end
+        rescue => failsafe
+          warn "RedisCacheStore ignored exception in handle_exception: #{failsafe.class}: #{failsafe.message}\n  #{failsafe.backtrace.join("\n  ")}"
+        end


Exceptions are swallowed by default. Apps provide an error_handler to report on them.

jeremy · 2017-11-13T04:36:43Z

activesupport/test/cache/stores/redis_cache_store_test.rb

+
+    test "write failure returns nil" do
+    end
+  end


matthewd · 2017-11-13T05:27:20Z

activesupport/CHANGELOG.md

+
+    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.


Is this advice consistent with it defaulting to redis://localhost:6379/0? 🤔

I initially set this up without a default for that reason, but it felt needlessly fussy for dev/test. I think clearly, repeatedly directing users to deployment guidance is the important ingredient.

Maybe we should default to some non-nil expiry, and then people heeding the "how to use this at its best" guidance can turn that off at the same time they point to a dedicated instance?

I like that direction since it require an informed choice of Redis usage mode.

Thing is, by default, Redis doesn't expire keys when it hits max mem—it returns errors. For expiry alone to work, we'd need to use volatile-lru/ttl max-mem policy instead of the default noeviction.

That suggests that we configure a volatile/allkeys policy on the cache store as well. Then we can inspect maxmemory-policy to satisfy ourselves that the server is on board with the user's intent.

matthewd · 2017-11-13T05:27:20Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+end
+
+require "digest/md5"
+require "active_support/core_ext/marshal"


md5 can be problematic; while it is slower, I think we should probably just use sha2.

matthewd · 2017-11-13T05:27:20Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+        else
+          super
+        end
+      end


Is it worth checking this when we connect? I remember a rescue-covered block used to be fairly expensive to enter, regardless of whether the exception ever occurred... but maybe my memory's out of date?

matthewd · 2017-11-13T05:27:20Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+            raise ArgumentError, "Only Redis glob strings are supported: #{matcher.inspect}"
+          end
+        end
+      end


Seems fine, but that would imply this method isn't "Cache Store API implementation".

matthewd · 2017-11-13T05:27:20Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+      # Removes expired entries. Not supported.
+      def cleanup(options = nil)
+        super
+      end


Is expiry not supported at all? Or is expiry not used by default, and then when it is, delegated to redis? (Meaning this method would be a no-op, but would be "working")

matthewd · 2017-11-13T05:27:20Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+        # For compat with the wexpected options hash argument.
+        def write_entry(key, entry, options = nil)
+          write_entry_kwargs key, entry, **options
+        end


Don't these have identical arities? 😕

matthewd · 2017-11-13T05:27:20Z

activesupport/lib/active_support/cache/redis_cache_store.rb

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


This does sound like a good idea, but I wonder whether it's up to the redis store to have that opinion. Seems more like it should be the global default (and then overridden for the in-memory store)?

matthewd · 2017-11-13T05:27:20Z

.travis.yml

@@ -41,7 +42,7 @@ before_script:
  # Decodes to e.g. `export VARIABLE=VALUE`
  - $(base64 --decode <<< "ZXhwb3J0IFNBVUNFX0FDQ0VTU19LRVk9YTAzNTM0M2YtZTkyMi00MGIzLWFhM2MtMDZiM2VhNjM1YzQ4")
  - $(base64 --decode <<< "ZXhwb3J0IFNBVUNFX1VTRVJOQU1FPXJ1YnlvbnJhaWxz")
-  - redis-server --bind 127.0.0.1 --port 6379 --requirepass 'password' --daemonize yes
+  - redis-server --bind 127.0.0.1 --port 6380 --requirepass 'password' --daemonize yes


Maybe we should have the test suite spin this up & down directly? Having to set a password on my local redis to get the tests to pass was annoying, but making everyone manually run a second instance seems even worse.

rafaelfranca · 2017-11-13T16:22:39Z

activesupport/lib/active_support/cache.rb

+            "#{namespace}:#{key}"
+          else
+            key
+          end
        end


This method was removed from public API in Rails 5.0. #22215 for context.

rafaelfranca · 2017-11-13T16:22:39Z

activesupport/lib/active_support/cache/redis_cache_store.rb

+  require "redis"
+  require "redis/distributed"
+rescue LoadError
+  warn "The Redis cache store requires the redis gem. Please add it to your Gemfile."


Should we be doing gem 'redis in this file so we assert the minimum version requirement?

Yes. I haven't carefully reviewed the oldest supported version yet. Will probably be Redis 3.3.0 with support for connect/read/write_timeout.

Actually, requiring latest redis-rb (4.0.1+) is appropriate for a new feature like this. Then sharded cache read_multi will just work without needing additional warnings.

rafaelfranca · 2017-11-13T17:57:01Z

activesupport/lib/active_support/cache.rb

+            "#{namespace}:#{key}"
+          else
+            key
+          end
        end


* 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 treated as misses and writes are dropped. * Local cache. Hot in-memory primary cache within block/middleware scope. * `read_/write_multi` support for Redis mget/mset. Use Redis::Distributed 4.0.1+ for distributed mget support. * `delete_matched` support for Redis KEYS globs.

jeremy · 2017-11-14T03:53:47Z

Thanks for review, @matthewd @rafaelfranca 🖖🏼

sorentwo · 2017-12-08T16:47:55Z

I'm a bit disappointed to see this from-scratch implementation considering all the effort that was put into https://github.com/sorentwo/readthis. It already supports every feature this implements, aside from distributed redis and local cache support.

Porting Readthis would have been a great way to get something that is well documented, tested, and has been used in production for years into Rails.

jkburges · 2018-01-10T03:02:12Z

I have a question about the syntax of the configuration, raised at https://stackoverflow.com/questions/48177606/ruby-syntax-error-unexpected-tlabel

I didn't think it was appropriate to discuss the question directly here, but hopefully ok to link to it, in case someone here can shed some light on it :-)

steakknife · 2018-05-04T04:27:41Z

@jkburges No biggie: it's not a function but an assignment. Surround the keys with braces. Should work.

its built in to rails now, see See rails/rails#31134 as well as https://bigbinary.com/blog/rails-5.2-adds-write_multi-for-cache-writes

jeremy force-pushed the redis-cache-store branch 7 times, most recently from 915bc90 to b1a47ad Compare November 13, 2017 03:19

jeremy commented Nov 13, 2017

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jeremy force-pushed the redis-cache-store branch from b1a47ad to a131987 Compare November 13, 2017 05:13

matthewd reviewed Nov 13, 2017

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jeremy force-pushed the redis-cache-store branch 3 times, most recently from a6aa479 to 1c0315e Compare November 13, 2017 07:33

jeremy mentioned this pull request Nov 13, 2017

Action Cable: run Redis tests against a default config without a password #31136

Merged

jeremy force-pushed the redis-cache-store branch 2 times, most recently from 2c5b5cf to bf7b7d7 Compare November 13, 2017 08:37

aeroastro mentioned this pull request Nov 13, 2017

Support expires_in in ActiveSupport::Cache::MemCacheStore#increment and #decrement #30716

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rafaelfranca reviewed Nov 13, 2017

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jeremy force-pushed the redis-cache-store branch from bf7b7d7 to 00a59bd Compare November 13, 2017 17:24

rafaelfranca approved these changes Nov 13, 2017

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activesupport/lib/active_support/cache.rb

"#{namespace}:#{key}"

else

key

end

end

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👍

jeremy force-pushed the redis-cache-store branch from 00a59bd to 31f51b3 Compare November 14, 2017 01:00

jeremy merged commit 9f8ec35 into rails:master Nov 14, 2017

jeremy deleted the redis-cache-store branch November 14, 2017 02:45

jeremy added this to the 5.2.0 milestone Nov 14, 2017

as3richa mentioned this pull request Mar 13, 2018

ActiveSupport::Cache::RedisCacheStore should support Redis instances for redis kwarg #32233

Closed

supercaracal mentioned this pull request Dec 24, 2018

Refactor and enhance Redis::Distributed redis/redis-rb#817

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olivierobert mentioned this pull request Oct 25, 2019

Rails Cache nimblehq/rails-templates#129

Open

mdallago mentioned this pull request Nov 11, 2019

Request api limit bitex-la/compliance#198

Merged

santiagorodriguez96 mentioned this pull request Aug 14, 2020

Add support for Ed25519 cedarcode/openssl-signature_algorithm#3

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zdavis mentioned this pull request Oct 28, 2020

Remove redis-rails gem ManifoldScholar/manifold#2876

Closed

rsanheim added a commit to simpledotorg/simple-server that referenced this pull request Feb 16, 2021

No need for redis-rails in rails 5.2

98c2c80

its built in to rails now, see See rails/rails#31134 as well as https://bigbinary.com/blog/rails-5.2-adds-write_multi-for-cache-writes

casperisfine mentioned this pull request Aug 18, 2021

Fix RedisCacheStore#write_multi to properly update the local store. #43042

Closed

unasuke mentioned this pull request Jan 12, 2022

Use ActiveSupport::Cache::RedisCacheStore if ActiveSupport > 5.2 joker1007/rukawa#47

Merged

alan-pie mentioned this pull request May 12, 2022

Inconsistency between Cache #increment behaviors #45069

Closed

Built-in Redis cache store #31134

Built-in Redis cache store #31134

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jeremy commented Nov 12, 2017

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jeremy commented Nov 14, 2017

sorentwo commented Dec 8, 2017

jkburges commented Jan 10, 2018

steakknife commented May 4, 2018