Unexplained Cache MISSes

Nigel Peck np.lists at sharphosting.uk
Wed May 31 19:45:14 CEST 2017

On 31/05/2017 09:49, Dridi Boukelmoune wrote:
> On Tue, May 30, 2017 at 8:06 PM, Nigel Peck <np.lists at sharphosting.uk> wrote:
>> Thanks, I'll look at that to make sure. The situation is, if I purge an
>> object, and that request is restarted in vcl_purge, it is by definition the
>> same object, is it not? Since it is the exact same request. So what I'm
>> saying is, about 10% of requests that I purge, receive a HIT on the restart
>> of that same request.
>> It's not because of intervening requests and I've not made any changes to
>> vcl_hash, so it's a very simple hash that isn't being changed before the
>> restart in vcl_purge.
> It is possible that while the purge is happening another client
> requests the same object and once the purge restarts into a GET or HIT
> it gets a hit from the other client's request.
> Grouping logs (by session or request) might help better understand
> what's happening. I haven't read this thread in details. Also please
> keep the list in CC.

Sorry about missing the list off the CC, was an oversight on my part, 
must have hit the wrong button and missed that I did that.

It's not due to other requests happening between. As Guillaume says the 
age is high, and also I checked many of these in varnishlog by looking 
at all entries for the URL and there is never a request in between.

Perhaps a good next step would be for me to set up a minimal install on 
a fresh CentOS 7 instance and see if I can reproduce there with minimal 
VCL? Although there is nothing in the VCL I have that should cause this 
intermittent behaviour.


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