Question about proxy cache when it expires

[Igor Sysoev]

On Tue, May 19, 2009 at 05:14:11PM +0200, J?r?me Loyet wrote:

> > On Tue, May 12, 2009 at 10:38:04AM +0200, J?r?me Loyet wrote:
> >
> >> Hello igor,
> >>
> >> I have a question about the cache behaviour in proxy mode.
> >>
> >> I have nginx in front head which redirect to an apache back end. Nginx
> >> caches eveything for M minutes.
> >>
> >> If I have a large number of requests for the same page and this page
> >> is cached : nginx returns the cached page ... no problems
> >> After M minutes, the cached page expires
> >> The first request coming after the expiration makes nginx to ask the
> >> backend for refresh
> >> When nginx receives the backend fresh response, it's saved to cache
> >> and then nginx serves the fresh cached page
> >>
> >> But what happen between the start of the request to the backend and
> >> the end of the response from the backend ? (let's assume that the
> >> backend serves the page in 5s ... and in 5s I can have a lot of
> >> request to this page).:
> >> - Are the request queued waiting for the backend response ?
> >> - Every request makes try to refresh the cache from the backend ? (in
> >> this case, I have multiple request for the same page to the backend
> >> ... I can have a burst of request and my apache can be overflowed by
> >> request -- that's why I'm using nignx with cache).
> >> - Do the requests serve the cached page even if it's expired until the
> >> backend response has been received ?
> >> - Maybe something else :)
> >
> > Currently all requests which found that a cached response expired
> > are proxied to backend. I plan to implement busy locks to pass the single
> > request and leave others to wait the response up to specified time.
> >
> 
> Hi igor,
> 
> about this feature. Do you know when you plan do implement it ? I
> really need this feature. If you don't have enough time, I can look
> into it if you explain to me briefly how you want to do it.

This is complex thing that I plan to implement in 0.8.


-- 
Igor Sysoev
http://sysoev.ru/en/