Cache timeout

[spirelli]

Could someone briefly explain to me the "Set cache timeout" option that can be set for each page? What exactly does this, and does it relate to the Cache that's within Contao (I believe there is something like this) or the browser cache? How do I work out what to set this to?

Many thanks!

[Andreas]

In Settings you can set "Bypass the internal cache", this is a cache for contao to run faster. You can see cached files on Maintenance "Purge the internal cache".

Cache for visitors:
In Settings you should set the cache mode to "use only the server cache" to ensure that your visitors always get the actual pages. But only pages with a cache time set will get cached. If you set a cache time for a page i.e. the "Website root" this settings gets inherited to subpages. Cached pages are stored in system/html/. Contaos page caching is not ment for simulating a static website. It is build to handle heavy server loads. So set it to a short time if you have many visitors.

[spirelli]

Thank you for your reply. I'd like to clarify:

The 'cache timeout' that I can set for each page, does this mean that the cache is being deleted and re-built after this amount of time? I don't quite understand why a shorter time would be better if the site has a lot of visitors.

Also, if an item gets changed in Contao – e.g. a piece of content, a file, or CSS – is the cache updated immediately with this change?

[Andreas]

The 'cache timeout' that I can set for each page, does this mean that the cache is being deleted and re-built after this amount of time?

Before Contao delivers a page it searches for an actual cached page. If cache time is set to 1 min and it finds a cached page, that isn't older than 1 min, this one gets delivered, else a new cached page version gets gernerated. If there are i.e. 100 page request within one min, the cached page gets delivered which is better as to build up this page a hundred times. After this minute a new version gets generated.

I don't quite understand why a shorter time would be better if the site has a lot of visitors.

Look above and there's a discussion on github (starts in german, further down in english). https://github.com/contao/core/issues/7155

Also, if an item gets changed in Contao – e.g. a piece of content, a file, or CSS – is the cache updated immediately with this change?

I don't think so but don't know exactly. Leo Feyer recommends to not try to simulate a static website because a CMS provides dynamic content. Just to use it for handling heavy loads.

ps When you're are logged into back end, pages will not get cached.