This feature allows URLs that usually are not visible by a visitor to be manipulated to enhance or respectively preserve cacheability.
To use the advanced cache control feature, enable the
advanced-cache-control option in your
<config> <acceleration> <advanced-cache-control [ low-precision-viewport="true" ] /> <acceleration> </config>
FIT usually tailors responses that are made for a unique client. For detecting those clients the most significant attribute is the
User-Agent request header. And because this header is so significant in creating a correct delivery context the responses by FIT are served with the header
Vary: User-Agent. This header can cause well known CDNs not to cache at all, which is particularly undesirable especially for data that could otherwise be cached publicly.
The unified caching mark - or short
ucm - combines all the relevant information that decisions made by FIT base on, i.e.
This information is aggregated in the ucm mark, which is added to URLs that are
<link rel="stylesheet" href="..."/>
allowUCMoption set to true
When a request to FIT contains a
ucm mark in the URL and the
advanced-cache-control setting is enabled in your configuration, FIT will calculate whether the information given by the client and the ucm in the URL match the information on the server.
If the information on client and server match FIT omits
Vary: User-Agent and instead uses
Cache-Control: public which usually is the most desired form of caching.
If the information on client and server do not match FIT omits the
Vary: User-Agent too, but instead will respond with
Varying viewport dimensions of resizeable browser requests lead to different
ucms, due to the diverse fitdetection cookies. This means, even though the window size might differ just slightly, the result is a different
ucm and therefore no matching client and server
To enhance the cacheability of resizeable browser requests the feature
low-precision-viewport can be enabled by setting it to
true. Different ranges of viewport dimensions are then grouped to defined breakpoints equalising the
ucm and increasing the matching client and server
false or setting no
low-precision-viewport attribute (default) leads to high precision
ucm marks and therefore less matching client and server
ucms, as the viewport dimensions have to match exactly.
Viewport dimensions can also vary because of horizontal scrollbars or other browser chrome elements with variable height (e.g. location bars). To minimize this influence on the UCM, set the
ignore-viewport-height attribute to
To make sure that FIT will not increase cacheability where it is not desired, consider enabling or disabling the
pass-cache-headers option in your