Determining a HIT or a MISS in Varnish 4 VCL

[Umesh Telang]

Thanks Raymond.

If we don't hear any views to the contrary from Varnish themselves, we'll go with the standard approach of using obj.hits

Regards,
Umesh

From: "<Jennings III>", Raymond <raymond.jennings at nytimes.com<mailto:raymond.jennings at nytimes.com>>
Date: Thursday, 2 April 2015 13:38
To: Umesh Telang <Umesh.Telang at bbc.co.uk<mailto:Umesh.Telang at bbc.co.uk>>
Cc: "varnish-misc at varnish-cache.org<mailto:varnish-misc at varnish-cache.org>" <varnish-misc at varnish-cache.org<mailto:varnish-misc at varnish-cache.org>>
Subject: Re: Determining a HIT or a MISS in Varnish 4 VCL

I think that's the way - exactly as you have in vcl_deliver.  I've always used that in V3 and now in V4 as well.

I'm suspect of that page telling you to not use obj in vcl_deliver but use that header value instead.

Raymond Jennings III
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On Thu, Apr 2, 2015 at 8:28 AM, Umesh Telang <Umesh.Telang at bbc.co.uk<mailto:Umesh.Telang at bbc.co.uk>> wrote:
Hello,

It's unclear if the way to detect whether a particular response was the result of a cache hit or miss in VCL, has changed from Varnish 3 to Varnish 4.

At this page (not an official Varnish page...), it suggests using the value of resp.http.X-Varnish (whether it has a single or multiple values) to determine this:
http://foshttpcache.readthedocs.org/en/latest/varnish-configuration.html#

Alternatively I've also seen suggestions for continuing to use obj.hits in vcl_deliver. e.g. :
sub vcl_deliver {
if (obj.hits > 0) { # Add debug header to see if it's a HIT/MISS and the number of hits, disable when not needed
set resp.http.X-Cache = "HIT";
} else {
set resp.http.X-Cache = "MISS";
}
}

We've observed that the value of %{Varnish:handling}x in the varnish ncsa log has been accurate in reporting HITs vs MISSes. Could we use a VCL equivalent of this in vcl_deliver to determine whether a particular response is the result of a HIT or a MISS?

Any advice on the recommended way in VCL to determine whether a response is the result of a HIT or MISS would be greatly appreciated!

Thanks,
Umesh

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