Merge branch 'redis-connection-pool' into 'master'

Redis connection pool

Split from https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3232

Having an easily accessible Redis connection pool allows us to do more
cool stuff with Redis in GitLab (instead of having to go through e.g.
the Rails cache).

See merge request !3521

Gemfile

@@ -149,6 +149,10 @@ gem 'version_sorter', '~> 2.0.0'
 # Cache
 gem "redis-rails", '~> 4.0.0'
 
+# Redis
+gem 'redis', '~> 3.2'
+gem 'connection_pool', '~> 2.0'
+
 # Campfire integration
 gem 'tinder', '~> 1.10.0'
 
@@ -229,7 +233,6 @@ group :metrics do
   gem 'allocations', '~> 1.0', require: false, platform: :mri
   gem 'method_source', '~> 0.8', require: false
   gem 'influxdb', '~> 0.2', require: false
-  gem 'connection_pool', '~> 2.0', require: false
 end
 
 group :development do

Gemfile.lock

@@ -999,6 +999,7 @@ DEPENDENCIES
   rdoc (~> 3.6)
   recaptcha
   redcarpet (~> 3.3.3)
+  redis (~> 3.2)
   redis-namespace
   redis-rails (~> 4.0.0)
   request_store (~> 1.3.0)

config/application.rb

@@ -4,11 +4,9 @@ require 'rails/all'
 require 'devise'
 I18n.config.enforce_available_locales = false
 Bundler.require(:default, Rails.env)
-require_relative '../lib/gitlab/redis_config'
+require_relative '../lib/gitlab/redis'
 
 module Gitlab
-  REDIS_CACHE_NAMESPACE = 'cache:gitlab'
-
   class Application < Rails::Application
     # Settings in config/environments/* take precedence over those specified here.
     # Application configuration should go into files in config/initializers
@@ -69,8 +67,8 @@ module Gitlab
       end
     end
 
-    redis_config_hash = Gitlab::RedisConfig.redis_store_options
-    redis_config_hash[:namespace] = REDIS_CACHE_NAMESPACE
+    redis_config_hash = Gitlab::Redis.redis_store_options
+    redis_config_hash[:namespace] = Gitlab::Redis::CACHE_NAMESPACE
     redis_config_hash[:expires_in] = 2.weeks # Cache should not grow forever
     config.cache_store = :redis_store, redis_config_hash
 

config/initializers/session_store.rb

@@ -13,7 +13,7 @@ end
 if Rails.env.test?
   Gitlab::Application.config.session_store :cookie_store, key: "_gitlab_session"
 else
-  redis_config = Gitlab::RedisConfig.redis_store_options
+  redis_config = Gitlab::Redis.redis_store_options
   redis_config[:namespace] = 'session:gitlab'
   
   Gitlab::Application.config.session_store(

config/initializers/sidekiq.rb

@@ -2,7 +2,7 @@ SIDEKIQ_REDIS_NAMESPACE = 'resque:gitlab'
 
 Sidekiq.configure_server do |config|
   config.redis = {
-    url: Gitlab::RedisConfig.url,
+    url: Gitlab::Redis.url,
     namespace: SIDEKIQ_REDIS_NAMESPACE
   }
 
@@ -29,7 +29,7 @@ end
 
 Sidekiq.configure_client do |config|
   config.redis = {
-    url: Gitlab::RedisConfig.url,
+    url: Gitlab::Redis.url,
     namespace: SIDEKIQ_REDIS_NAMESPACE
   }
 end

config/mail_room.yml

@@ -2,7 +2,7 @@
 <%
 require "yaml"
 require "json"
-require_relative "lib/gitlab/redis_config"
+require_relative "lib/gitlab/redis"
 
 rails_env = ENV["RAILS_ENV"] || ENV["RACK_ENV"] || "development"
 
@@ -18,7 +18,7 @@ if File.exists?(config_file)
   config['mailbox']    = "inbox"  if config['mailbox'].nil?
 
   if config['enabled'] && config['address']
-    redis_url = Gitlab::RedisConfig.new(rails_env).url
+    redis_url = Gitlab::Redis.new(rails_env).url
     %>
     -
       :host: <%= config['host'].to_json %>

lib/gitlab/exclusive_lease.rb

@@ -43,7 +43,9 @@ module Gitlab
     # false if the lease is already taken.
     def try_obtain
       # Performing a single SET is atomic
-      !!redis.set(redis_key, '1', nx: true, ex: @timeout)
+      Gitlab::Redis.with do |redis|
+        !!redis.set(redis_key, '1', nx: true, ex: @timeout)
+      end
     end
 
     # No #cancel method. See comments above!

lib/gitlab/redis_config.rb → lib/gitlab/redis.rb

 module Gitlab
-  class RedisConfig
+  class Redis
+    CACHE_NAMESPACE = 'cache:gitlab'
+
     attr_reader :url
 
+    # To be thread-safe we must be careful when writing the class instance
+    # variables @url and @pool. Because @pool depends on @url we need two
+    # mutexes to prevent deadlock.
+    URL_MUTEX = Mutex.new
+    POOL_MUTEX = Mutex.new
+    private_constant :URL_MUTEX, :POOL_MUTEX
+
     def self.url
-      new.url
+      @url || URL_MUTEX.synchronize { @url = new.url }
+    end
+
+    def self.with
+      if @pool.nil?
+        POOL_MUTEX.synchronize do
+          @pool = ConnectionPool.new { ::Redis.new(url: url) }
+        end
+      end
+      @pool.with { |redis| yield redis }
     end
     
     def self.redis_store_options
       url = new.url
-      redis_config_hash = Redis::Store::Factory.extract_host_options_from_uri(url)
+      redis_config_hash = ::Redis::Store::Factory.extract_host_options_from_uri(url)
       # Redis::Store does not handle Unix sockets well, so let's do it for them
       redis_uri = URI.parse(url)
       if redis_uri.scheme == 'unix'

lib/tasks/cache.rake

@@ -4,18 +4,19 @@ namespace :cache do
 
   desc "GitLab | Clear redis cache"
   task :clear => :environment do
-    redis = Redis.new(url: Gitlab::RedisConfig.url)
-    cursor = REDIS_SCAN_START_STOP
-    loop do
-      cursor, keys = redis.scan(
-        cursor,
-        match: "#{Gitlab::REDIS_CACHE_NAMESPACE}*", 
-        count: CLEAR_BATCH_SIZE
-      )
-
-      redis.del(*keys) if keys.any?
-
-      break if cursor == REDIS_SCAN_START_STOP
+    Gitlab::Redis.with do |redis|
+      cursor = REDIS_SCAN_START_STOP
+      loop do
+        cursor, keys = redis.scan(
+          cursor,
+          match: "#{Gitlab::Redis::CACHE_NAMESPACE}*", 
+          count: CLEAR_BATCH_SIZE
+        )
+  
+        redis.del(*keys) if keys.any?
+  
+        break if cursor == REDIS_SCAN_START_STOP
+      end
     end
   end
 end