Let varnish send old data from cache while it's fetching a new one?
- by mark
I'm caching dynamically generated pages (PHP-FPM, NGINX) and have varnish in front of them, this works very well.
However, once the cache timeout is reached, I see this:
new client requests page
varnish recognizes the cache timeout
client waits
varnish fetches new page from backend
varnish delivers new page to the client (and has page cached, too, for the next request which gets it instantly)
What I would like to do is:
client requests page
varnish recognizes the timeout
varnish delivers old page to the client
varnish fetches new page from backend and puts it into the cache
In my case it's not site where outdated information is such a big problem, especially not when we're talking about cache timeout from a few minutes.
However, I don't want punish user to wait in line and rather deliver something immediate. Is that possible in some way?
To illustrate, here's a sample output of running siege 5 minutes against my server which was configured to cache for one minute:
HTTP/1.1,200, 1.97, 12710,/,1,2013-06-24 00:21:06
...
HTTP/1.1,200, 1.88, 12710,/,1,2013-06-24 00:21:20
...
HTTP/1.1,200, 1.93, 12710,/,1,2013-06-24 00:22:08
...
HTTP/1.1,200, 1.89, 12710,/,1,2013-06-24 00:22:22
...
HTTP/1.1,200, 1.94, 12710,/,1,2013-06-24 00:23:10
...
HTTP/1.1,200, 1.91, 12709,/,1,2013-06-24 00:23:23
...
HTTP/1.1,200, 1.93, 12710,/,1,2013-06-24 00:24:12
...
I left out the hundreds of requests running in 0.02 or so. But it still concerns me that there are going to be users having to wait almost 2 seconds for their raw HTML.
Can't we do any better here?
(I came across Varnish send while cache , it sounded similar but not exactly what I'm trying to do.)
