Fix slow query of federated timeline (#12886)

db/migrate/20200119112504_add_public_index_to_statuses.rb

@@ -0,0 +1,11 @@
+class AddPublicIndexToStatuses < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def up
+    add_index :statuses, [:id, :account_id], name: :index_statuses_public_20200119, algorithm: :concurrently, order: { id: :desc }, where: 'deleted_at IS NULL AND visibility = 0 AND reblog_of_id IS NULL AND ((NOT reply) OR (in_reply_to_account_id = account_id))'
+  end
+
+  def down
+    remove_index :statuses, name: :index_statuses_public_20200119
+  end
+end