Fix account counters being overwritten by parallel writes (#12045)

db/migrate/20191001213028_add_lock_version_to_account_stats.rb

@@ -0,0 +1,15 @@
+require Rails.root.join('lib', 'mastodon', 'migration_helpers')
+
+class AddLockVersionToAccountStats < ActiveRecord::Migration[5.2]
+  include Mastodon::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  def up
+    safety_assured { add_column_with_default :account_stats, :lock_version, :integer, allow_null: false, default: 0 }
+  end
+
+  def down
+    remove_column :account_stats, :lock_version
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2019_09_27_232842) do
+ActiveRecord::Schema.define(version: 2019_10_01_213028) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -97,6 +97,7 @@ ActiveRecord::Schema.define(version: 2019_09_27_232842) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.datetime "last_status_at"
+    t.integer "lock_version", default: 0, null: false
     t.index ["account_id"], name: "index_account_stats_on_account_id", unique: true
   end