Making a dummy request to the backend on cache hit

Connor Walls connor.walls at
Wed Aug 3 15:29:34 CEST 2011


I've had a look around the VCL documentation, and I reckon this will probably only be possible by using inline C, but I wanted to make sure. We're having a minor issue in that whenever an object is served from the cache, the lack of a request to the backend server means that the server is unable to record a log for that page being accessed (as is to be expected). A possible solution that has been put forward is to make a sort of "dummy" request to the backend whenever the cache is hit, i.e. the user is served a page from the cache (so the user gets the content immediately), and a request is made to the backend server, with a particular header or variable that tells the backend not to attempt to render the page, merely to record the request in the logs.

Is this something that is feasible in vanilla VCL, or would it require inline C? Are there any obvious problems to this that I'm not seeing? The main issue I see being that the request volume to the backend server will remain high even with content being served from the cache, but with the server not performing any rendering or serving any content, I reckon this will be a minor issue.

Thanks in advance for any help,

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