Varnish 4.1.4 - MAIN.n_gunzip counter increasing for every MAIN.backend_req

Dridi Boukelmoune dridi at
Fri Jan 6 14:07:32 CET 2017

On Fri, Jan 6, 2017 at 10:28 AM, Vlad Rusu <vlad.rusu at> wrote:
> Hi guys,
> Gzip tag, in the format section, shows a possible flag of ‘u’ representing a
> Gunzip-test
> In my varnishstat output I see how MAIN.n_gunzip equals (roughly)
> MAIN.backend_req
> Looking at the Gzip tag, I see the following for every backend request:
> Gzip           u F - 70 55 80 80 489
> Can someone help me understand what a Gunzip-test means / does? It sure gets
> counted against MAIN.n_gunzip.

Hello Vlad,

The gunzip test is performed when an already-gzipped backend response
is inserted in the cache. It is inflated in a black-hole, only to make sure
that the object being fetched is proper gzip.

> Am not attaching the VCL or a full varnishstat as I don’t think it makes
> sense. Each backend sends gzipped data back to Varnish and each client
> requests for gzipped data from Varnish..

For each gzipped backend response, you will see this behavior (u flag
in logs, and counter increment). There is no separate counter for test
gunzip vs regular gunzip, although some of us would like to make the

As an end-user, how and where would this be best documented in your

Best Regards,

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