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 <j...@7fff.com> 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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