Fix slow local timeline query (#11648)

Fix #11643

db/migrate/20190823221802_add_local_index_to_statuses.rb

@@ -0,0 +1,11 @@
+class AddLocalIndexToStatuses < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def up
+    add_index :statuses, [:id, :account_id], name: :index_statuses_local_20190824, algorithm: :concurrently, order: { id: :desc }, where: '(local OR (uri IS NULL)) AND 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_local_20190824
+  end
+end