..tip::

Accessing flash messages means that the session must be started, which

in turn will cause Symfony to mark the responses as ``private``. In general,

since flashes shall displayed only once, pages that might display flashes

cannot reasonably be cached in HTTP caches.

Accessing flash messages requires starting the session, which in turn

causes Symfony to mark the response as ``private``. In general, because

flash messages are meant to be displayed only once, pages that might show

them cannot reasonably be cached by HTTP caches.

As an alternative, you can load flash messages asynchronously through

another HTTP request (for example, using a `Twig Live Component`_), making

the original page fully cacheable.

Configuration

can use the Symfony save handler without side effects and that the session

has not been started before Symfony is initialized.

.. _`Twig Live Component`:https://symfony.com/bundles/ux-live-component/current/index.html

.. _`phpredis extension`:https://github.com/phpredis/phpredis

.. _`DoctrineMongoDBBundle configuration`:https://symfony.com/doc/master/bundles/DoctrineMongoDBBundle/config.html

.. _`MongoDB shell`:https://docs.mongodb.com/manual/mongo/