BUGFIX: properly reconnect to the current db after forking

lib/discourse.rb

@@ -238,11 +238,12 @@ module Discourse
   # after fork, otherwise Discourse will be
   # in a bad state
   def self.after_fork
+    current_db = RailsMultisite::ConnectionManagement.current_db
+    RailsMultisite::ConnectionManagement.establish_connection(db: current_db)
+    MessageBus.after_fork
     SiteSetting.after_fork
-    ActiveRecord::Base.establish_connection
     $redis.client.reconnect
     Rails.cache.reconnect
-    MessageBus.after_fork
     # /!\ HACK /!\ force sidekiq to create a new connection to redis
     Sidekiq.instance_variable_set(:@redis, nil)
   end

lib/export/exporter.rb

@@ -144,6 +144,7 @@ module Export
       pg_dump_running = true
 
       Thread.new do
+        RailsMultisite::ConnectionManagement::establish_connection(db: @current_db)
         while pg_dump_running
           message = logs.pop.strip
           log(message) unless message.blank?