silverstripe-framework/docs/en/02_Developer_Guides/08_Performance/02_HTTP_Cache_Headers.md

title: HTTP Cache Headers summary: Set the correct HTTP cache headers for your responses.

Caching Headers

By default, PHP adds caching headers that make the page appear purely dynamic. This isn't usually appropriate for most sites, even ones that are updated reasonably frequently. SilverStripe overrides the default settings with the following headers:

• The Last-Modified date is set to be most recent modification date of any database record queried in the generation of the page.
• The Expiry date is set by taking the age of the page and adding that to the current time.
• Cache-Control is set to max-age=86400, must-revalidate
• Since a visitor cookie is set, the site won't be cached by proxies.
• Ajax requests are never cached.

Customizing Cache Headers

HTTP::set_cache_age

:::php
HTTP::set_cache_age(0);

Used to set the max-age component of the cache-control line, in seconds. Set it to 0 to disable caching; the "no-cache" clause in Cache-Control and Pragma will be included.

HTTP::register_modification_date

:::php
HTTP::register_modification_date('2014-10-10');

Used to set the modification date to something more recent than the default. [api:DataObject::__construct] calls [api:HTTP::register_modification_date(] whenever a record comes from the database ensuring the newest date is present.

Vary: cache header

By default, SilverStripe will output a Vary header (used by upstream caches for determining uniqueness) that looks like

Cookie, X-Forwarded-Protocol, User-Agent, Accept

To change the value of the Vary header, you can change this value by specifying the header in configuration

HTTP:
  vary: ""