Prefetching / Prefetchable – Knowledge Base

Since Januar 2014 you can find a new option in the Luna Property Manager called 'prefetchable' (https://control.akamai.com/dl/customers/LUNA/ReleaseNotes/2014/LunaReleaseNotes0114.pdf or in the documentation https://control.akamai.com/dl/customers/other/EDGESERV/ESConfigGuide-Customer.pdf chapter 210).

The 'prefetchable" option extended the already existing 'prefetching' option. Although there is a short help text poping up in Property Manager a lot of people are not sure about the difference between 'prefetching' and 'prefetchable', so let put a little light on this issue:

Prefetching is parsing the HTML BEFORE it is delivered to the client for assets like pics, css and js. In case Akamai finds existing URLs those can get pro-activly loaded before the client calls those URLs

Prefetchable can define a prefetch for a defined file-extension

Keep in mind that prefetching will cause additional midgress-traffic.

Prefetch objects can be identified via X-Akamai-Prefetched-Object :

When Prefetching is enabled, the Akamai server retrieves images and scripts embedded in HTML content at the same time it serves the HTML to the browser, rather than waiting for the browser to request these objects. This can significantly decrease the overall rendering time of the HTML page.

Prefetching can be applied to either cacheable or uncacheable content. When Prefetching is used for cacheable content, and the object to be prefetched is already in cache, the object is moved from disk into memory so that it is ready to be served. When used for uncacheable content, prefetching causes the retrieved objects to be uniquely associated with the client browser request that triggered the prefetch so that these objects cannot be served to a different end user. Prefetching can be combined with Tiered Distribution to further improve the speed of object delivery and to protect the origin server from bursts of prefetch traffic. When Prefetching is used for cacheable content, you are strongly encouraged to configure Tiered Distribution for the content as well.

By default, objects are “no-stored" that is, not cached for your application on the Akamai edge servers. However, Akamai caches objects with certain file extensions by default. These objects include text, image, style sheet, and audio files among others. They may be fragments of parent pages to be fetched either from cache or from the origin by an edge server in order to reduce latency in delivering content to the end user. You can add and remove objects from this list as required. These same objects become the objects to be prefetched by default.

At the origin, you can identify the prefetch objects by the special header, X-Akamai-Prefetched-Object, that edge servers associate with every prefetch request. The value of this header is not used; it is the presence of the header itself that indicates a prefetch request.

At the origin, you can identify the prefetch objects by the special header, X-Akamai-Prefetched-Object, that edge servers associate with every prefetch request. The value of this header is not used; it is the presence of the header itself that indicates a prefetch request.

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