cache: replace memcache with redis.

Drop memcache. Use redis for all caching instead.

config/initializers/cache_store.rb

@@ -0,0 +1,26 @@
+Rails.application.configure do
+  if Rails.env.test?
+    cache_config = [:memory_store, { size: 32.megabytes }]
+  else
+    cache_config = [
+      :redis_cache_store,
+      {
+        url: Danbooru.config.redis_url,
+        namespace: nil,
+        connect_timeout:   30, # default: 20 seconds
+        write_timeout:    0.2, # default: 1 second
+        read_timeout:     0.2, # default: 1 second
+        reconnect_attempts: 0, # default: 0
+        error_handler: ->(method:, returning:, exception:) {
+          DanbooruLogger.log(exception, method: method, returning: returning)
+        }
+      }
+    ]
+  end
+
+  cache_store = ActiveSupport::Cache.lookup_store(cache_config)
+
+  config.cache_store = cache_store
+  config.action_controller.cache_store = cache_store
+  Rails.cache = cache_store
+end

config/initializers/z_dalli.rb

@@ -1,28 +0,0 @@
-Rails.application.configure do
-  begin
-    if Rails.env.test?
-      config.cache_store = :memory_store, { size: 32.megabytes }
-      config.action_controller.cache_store = :memory_store, { size: 32.megabytes }
-      Rails.cache = ActiveSupport::Cache.lookup_store(Rails.application.config.cache_store)
-    else
-      config.cache_store = :dalli_store, Danbooru.config.memcached_servers, { namespace: Danbooru.config.safe_app_name }
-      config.action_controller.cache_store = :dalli_store, Danbooru.config.memcached_servers, { namespace: Danbooru.config.safe_app_name }
-      Rails.cache = ActiveSupport::Cache.lookup_store(Rails.application.config.cache_store)
-
-      Rails.cache.dalli.alive!
-    end
-  rescue Dalli::RingError => e
-    puts "-" * 40
-    puts "WARNING! MEMCACHE SERVER NOT FOUND! You will experience performance degradation."
-    puts e.to_s
-    puts "-- BEGIN STACKTRACE --"
-    e.backtrace.each do |line|
-      puts line
-    end
-    puts "-- END STACKTRACE --"
-    puts "-" * 40
-
-    config.cache_store = :memory_store, { size: 32.megabytes }
-    Rails.cache = ActiveSupport::Cache.lookup_store(Rails.application.config.cache_store)
-  end
-end