Add Rake task to clean up unused multisite Redis keys.

app/jobs/scheduled/clean_up_redis_keys.rb

@@ -0,0 +1,37 @@
+module Jobs
+  class CleanUpRedisKeys < Jobs::Scheduled
+    every 1.week
+
+    def execute(args)
+      return unless Rails.configuration.multisite
+      return unless SiteSetting.clean_up_redis_keys
+
+      dbs = RailsMultisite::ConnectionManagement.all_dbs
+      dbs << Discourse::SIDEKIQ_NAMESPACE
+
+      regexp = /((\$(?<message_bus>\w+)$)|(^?(?<namespace>\w+):))/
+
+      cursor = 0
+      redis = $redis.without_namespace
+
+      loop do
+        cursor, keys = redis.scan(cursor)
+        cursor = cursor.to_i
+
+        redis.multi do
+          keys.each do |key|
+            if match = key.match(regexp)
+              db_name = match[:message_bus] || match[:namespace]
+
+              if !dbs.include?(db_name)
+                redis.del(key)
+              end
+            end
+          end
+        end
+
+        break if cursor == 0
+      end
+    end
+  end
+end

lib/discourse.rb

@@ -371,9 +371,11 @@ module Discourse
     end
   end
 
+  SIDEKIQ_NAMESPACE ||= 'sidekiq'.freeze
+
   def self.sidekiq_redis_config
     conf = GlobalSetting.redis_config.dup
-    conf[:namespace] = 'sidekiq'
+    conf[:namespace] = SIDEKIQ_NAMESPACE
     conf
   end
 

spec/tasks/redis_spec.rb

@@ -0,0 +1,45 @@
+require 'rails_helper'
+
+RSpec.describe "Redis rake tasks" do
+  let(:redis) { $redis.without_namespace }
+
+  before do
+    @multisite = Rails.configuration.multisite
+    Rails.configuration.multisite = true
+    Discourse::Application.load_tasks
+  end
+
+  after do
+    Rails.configuration.multisite = @multisite
+  end
+
+  describe 'clean up' do
+    it 'should clean up orphan Redis keys' do
+      active_keys = [
+        '__mb_backlog_id_n_/users/someusername$|$default',
+        'default:user-last-seen:607',
+        'sidekiq:something:do:something',
+        'somekeytonotbetouched'
+      ]
+
+      orphan_keys = [
+        'tgxworld:user-last-seen:607',
+        '__mb_backlog_id_n_/users/someusername$|$tgxworld'
+      ]
+
+      (active_keys | orphan_keys).each do |key|
+        redis.set(key, 1)
+      end
+
+      Rake::Task['redis:clean_up'].invoke
+
+      active_keys.each do |key|
+        expect(redis.get(key)).to eq('1')
+      end
+
+      orphan_keys.each do |key|
+        expect(redis.get(key)).to eq(nil)
+      end
+    end
+  end
+end