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https://github.com/silverstripe/silverstripe-framework
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26 lines
1.5 KiB
Markdown
26 lines
1.5 KiB
Markdown
# Cache control
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By default, PHP add caching headers that make the page appear "purely dynamic".
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This isn't usually appropriate for most sites, even ones that are updated reasonably frequently.
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In particular, the default PHP cache-control settings prevent sites from appearing in the internet archive.
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SilverStripe overrides the default settings with the following:
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Default setting:
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* The `Last-Modified` date is set to be most recent modification date of any database record queried in the generation of the page.
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* The `Expiry` date is set by taking the age of the page and adding that to the current time.
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* `Cache-Control` is set to `max-age=86400, must-revalidate`
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* Since a visitor cookie is set, the site won't be cached by proxies
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* Ajax requests are never cached.
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Overriding these defaults
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* `[api:HTTP::$cache_age]` can be used to set the max-age component of the cache-control line, in seconds.
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Set it to 0 to disable caching; the "no-cache" clause in `Cache-Control` and `Pragma` will be included. It works only for live sites, if `SS_ENVIRONMENT_TYPE` is set to "dev" `[api:HTTP::$cache_age]` will be always overridden with 0.
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* `[api:HTTP::register_modification_date()]` can be used to set the modification date to something more recent than the default.
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How it works:
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* `[api:DataObject::__construct()]` calls `[api:HTTP::register_modification_date()]` whenever a record comes from the database
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* `Controller::run()` calls `[api:HTTP::add_cache_headers()]` before outputting the page
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