Question about proxy cache when it expires
jerome at loyet.net
Tue May 19 19:14:11 MSD 2009
> 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.
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.
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