Question from Dec. 2009: "still using cache when fetching content"

John Norman john at
Fri Jan 8 22:35:47 CET 2010

I think Chris Davies has straightened me out, and that the scenario I
describe *is* covered by grace -- that the first hit would also get stale
(as well as others in the grace period), which is exactly what I want.

On Fri, Jan 8, 2010 at 4:20 PM, John Norman <john at> wrote:

> Hi. I've just subscribed, and have been reading through the e-mail archives
> for varnish-misc.
> In Dec. 2009, Jean-Christophe Petit asked (with subject "still using cache
> when fetching content"):
> -----
> Is it possible to make Varnish sending the cache content at the same
> time it is fetching from the backend ?
> It will be more efficient for slow dynamic content ;)
> For example, I have a php page taking up to 5sec to run. If Varnish was
> able to get it while still sending the old cache page, it would be
> really great.
> No more unlucky visitor hitting it to update the cache..
> -----
> There were a couple of replies, but I just wanted to flesh out the "use
> case":
> I think the scenario would be:
> (1) There is a page that takes a very long time to render (say, 90 seconds)
> (2) It is cached, perhaps to expire after an hour
> (3) In normal usage, everyone gets the cached page and is very happy
> (4) An administrator would like to refresh that page in the cache BEFORE
> the hour is up; but give any user the earlier cached page
> (6) The admin would like a mechanism: "Please refresh now with this
> request, but until the request is finished, serve whatever is in the cache."
> This is different from grace, 'cos no one (except the admin) is incurring
> the wait; and also the admin is asking for a refresh before the cached page
> has expired.
> Is this a feature that can be simulated in Varnish? Or a feature that might
> be added at some time?
> What we're concerned about is Google's timing of page download. If we set a
> cache period to, say, an hour, and Google incurs the "first hit" after cache
> expiry, then it (Google) has to wait for the finished page. In grace mode,
> requests after the Google hit would get the earlier cached page; but, still,
> Google has measured the page as taking, say, 60 seconds to download. In the
> model above, Google would get the cached page; it would just be stale.
> Thoughts?
> John
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