Question about proxy cache when it expires

[Igor Sysoev]

On Wed, May 20, 2009 at 02:32:39PM +0200, J?r?me Loyet wrote:

> OK
> 
> I'll try to look into the code to see what I can do. Do you have any
> lead to guide me on this quest ? :)

This is complex thing. It requires sending notifications from one worker
to another when busy lock is being freed.

> 2009/5/20 Igor Sysoev <is at rambler-co.ru>:
> > 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/
> >
> >

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