Add rake task to clean up orphane Redis keys when a multisite has been removed.

lib/tasks/redis.rake

@@ -0,0 +1,30 @@
+task 'redis:clean_up' => ['environment'] do
+  return unless Rails.configuration.multisite
+
+  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