[webkit-dev] X-Purpose on prefetching requests

[Gavin Peters (蓋文彼德斯)]

On 28 September 2010 20:25, Alexey Proskuryakov <ap at webkit.org> wrote:
>
> 28.09.2010, в 17:07, Gavin Peters (蓋文彼德斯) написал(а):
>
>> If you're questioning if prefetch can make page loads faster, I can
>> say that on the web today it does.
>
> Thank you for the information.
>
> Does the performance increase come at the cost of correctness? I.e., are these sites requiring revalidation on each load?

That's a great question, and I don't have data on it in aggregate.
The only examples I know of for pages varying behaviour based on the
X-Moz header are sites that deny prefetches.

I hope that revalidation will end up being somewhat rare: adding a RTT
to the root document of a page of course slows down first paint,
onload, etc.. by pretty much exactly one RTT.  If correctness requires
it, so be it, but if a resource would have been cacheable on a
user-initiated load, I hope site operators would allow it to be
cacheable for prefetchers over the same period.  Of course, this is
the default behaviour now, and it's the one that webkit enforces.

>
>> The samples of prefetching on the web today are mostly cross site.
>
> Can you provide any examples?

Yes.  Google Web Search provides a prefetch link to the first search
result in many cases.  These links are (almost?) always cross site.

- Gavin