Extract counters from accounts table to account_stats table (#9295)

db/post_migrate/20181116184611_copy_account_stats_cleanup.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+class CopyAccountStatsCleanup < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def change
+    safety_assured do
+      remove_column :accounts, :statuses_count, :integer, default: 0, null: false
+      remove_column :accounts, :following_count, :integer, default: 0, null: false
+      remove_column :accounts, :followers_count, :integer, default: 0, null: false
+    end
+  end
+end