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From Otto van der Schaaf <osch...@we-amp.com>
Subject Re: Emitting Cache-Control: immutable
Date Wed, 29 Nov 2017 15:18:13 GMT
Quoting one of the comments from Patrick McManus:

*"The core concept is that without immutable the concepts of fresh and
current are*
*not clearly separated. http caching allows for fresh (i.e. cache
replayable) data *
*that isn’t the most current representation of a resource – and of course
firefox *
*normally uses that. But when you press refresh we in the past have
revalidated *
*even fresh things (i.e. with a high max age) to check to see if they were
still the *
*most current. immutable lets the cache know that there is never more than
1 *
*version of that resource, so we only need to worry about freshness and
never *
*re-validate under those circumstances."*

>From what I understand the behavior of browsers should change when pages are
reloaded, for any resources linked that have cache-control: immutable.

But.. I just tested, and I can not confirm that Chrome actually uses
revalidation
when I reload pages with cache-extended resources over at modpagespeed.com.
It pulls them from its cache instead.
So it looks like this needs some more testing with other browsers, and
perhaps
proxies, to see if there are clear advantages.

Otto


On Wed, Nov 29, 2017 at 3:31 PM Joshua Marantz <jmarantz@google.com.invalid>
wrote:

> This sounds like a reasonable idea to me.  I agree that .pagespeed. URLs
> are a good candidate for this, as long as the hash is matching and
> therefore we are sending 1-year caching directives.
>
> However I'm confused why about why revalidation would be needed in such
> cases, even without 'immutable', unless the item has been in cache for >1
> year.
>
>
> On Thu, Nov 23, 2017 at 3:33 PM, Otto van der Schaaf <oschaaf@we-amp.com>
> wrote:
>
> > Hi all,
> >
> > I wanted to discuss emitting the "immutable" cache-control directive in
> > responses for requests to .pagespeed. urls.
> >
> > After reading up on this fairly new cache-control directive, think we may
> > be able to avoid revalidations by doing so.
> > The RFC mentions versioned urls as a candidate for doing this, which I
> > think also includes our fingerprinted .pagespeed. urls
> > (these have a hash that changes when any of the underlying resources
> > change)
> >
> > Rough implementation:
> > https://github.com/pagespeed/mod_pagespeed/compare/oschaaf-
> > cc-immutable?expand=1
> >
> > Context:
> > https://hacks.mozilla.org/2017/01/using-immutable-
> > caching-to-speed-up-the-web/
> > https://tools.ietf.org/html/rfc8246
> >
> > Would love to hear thoughts on this!
> >
> > Otto
> >
>

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