[squid-users] Objects with values below 60 second for Cache-Control max-age are not cached

[Garri Djavadyan]

Sorry, Amos, it seems my latest reply was ambiguous. I tried to inform,
that while debugging the issue I have found the cause. It was default
value for 'minimum_expire_time'.


On Wed, 2016-10-26 at 23:58 +1300, Amos Jeffries wrote:
> On 26/10/2016 7:21 p.m., Garri Djavadyan wrote:
> > 
> > On Wed, 2016-08-24 at 19:09 +0500, Garri Djavadyan wrote:
> > > 
> > > On Mon, 2016-08-22 at 16:46 +0500, Garri Djavadyan wrote:
> > > > 
> > > > 
> > > > Hello Squid users,
> > > > 
> > > > Can anyone explain, why Squid doesn't cache the objects with
> > > > max-
> > > > age
> > > > values below 60 seconds?
> 
> Several possible reasons...
> 
> > 
> > For example:
> > > 
> > > > 
> > > > 
> > > > $ http_proxy="127.0.0.1:3128" curl --head "http://sandbox.comne
> > > > t.lo
> > > > ca
> > > > l/
> > > > cgi-bin/hello.cgi" && date
> > > > HTTP/1.1 200 OK
> > > > Date: Mon, 22 Aug 2016 11:31:16 GMT
> > > > Server: Apache
> > > > Cache-Control: max-age=60
> > > > Content-Type: text/plain
> > > > X-Cache: MISS from gentoo.comnet.uz
> > > > Via: 1.1 gentoo.comnet.uz (squid/3.5.20)
> > > > Connection: keep-alive
> > > > 
> > > > Mon Aug 22 16:31:19 UZT 2016
> > > > 
> 
> 1) This is not a GET request.
> 
> There is no object data returned on a HEAD request. So Squid does not
> have anything to cache.
> 
> If you did a GET before this request, then the caching time is
> relative
> to that request, not this one.

It is not true. Squid successfully caches HEAD requests.

$ for i in 1 2 ; do http_proxy="127.0.0.1:3128" \
curl --head http://sandbox.comnet.local/cgi-bin/5mb.cgi \
2>/dev/null | grep X-Cache; done

X-Cache: MISS from gentoo.comnet.uz
X-Cache: HIT from gentoo.comnet.uz


> 2) There is no Last-Modified header.
> 
> Squid older than 3.5.22 do not revalidate properly with only a Date
> header. Meaning new content is required fetching if the cached object
> was stale.

'Date' + 'Cache-Control: max-age=70' worked as expected.
'Date' + 'Cache-Control: max-age=60' does not worked.


> 3) The response to a HEAD request is supposed to be the headers that
> would be sent in an equivalent GET. So the servers upstream response
> headers are the right output here in light of (2) and/or (1).
> 
> > 
> > > 
> > > > 
> > > > ---
> > > > 
> > > > $ http_proxy="127.0.0.1:3128" curl --head "http://sandbox.comne
> > > > t.lo
> > > > ca
> > > > l/
> > > > cgi-bin/hello.cgi" && date
> > > > HTTP/1.1 200 OK
> > > > Date: Mon, 22 Aug 2016 11:31:23 GMT
> > > > Server: Apache
> > > > Cache-Control: max-age=60
> > > > Content-Type: text/plain
> > > > X-Cache: MISS from gentoo.comnet.uz
> > > > Via: 1.1 gentoo.comnet.uz (squid/3.5.20)
> > > > Connection: keep-alive
> > > > 
> > > > Mon Aug 22 16:31:26 UZT 2016
> > > > 
> > > > 
> > > > No problems with values above 60 seconds. For example:
> > > > 
> > > > $ http_proxy="127.0.0.1:3128" curl --head "http://sandbox.comne
> > > > t.lo
> > > > ca
> > > > l/
> > > > cgi-bin/hello.cgi" && date
> > > > HTTP/1.1 200 OK
> > > > Date: Mon, 22 Aug 2016 11:36:06 GMT
> > > > Server: Apache
> > > > Cache-Control: max-age=70
> > > > Content-Type: text/plain
> > > > X-Cache: MISS from gentoo.comnet.uz
> > > > Via: 1.1 gentoo.comnet.uz (squid/3.5.20)
> > > > Connection: keep-alive
> > > > 
> > > > Mon Aug 22 16:36:09 UZT 2016
> > > > 
> > > > ---
> > > > 
> > > > $ http_proxy="127.0.0.1:3128" curl --head "http://sandbox.comne
> > > > t.lo
> > > > ca
> > > > l/
> > > > cgi-bin/hello.cgi" && date
> > > > HTTP/1.1 200 OK
> > > > Date: Mon, 22 Aug 2016 11:36:06 GMT
> > > > Server: Apache
> > > > Cache-Control: max-age=70
> > > > Content-Type: text/plain
> > > > Age: 5
> > > > X-Cache: HIT from gentoo.comnet.uz
> > > > Via: 1.1 gentoo.comnet.uz (squid/3.5.20)
> > > > Connection: keep-alive
> > > > 
> > > > Mon Aug 22 16:36:11 UZT 2016
> > > > 
> > > > 
> > > > As you can see, time difference between origin server and
> > > > localhost
> > > > is
> > > > 3 seconds (UZT is +5 offset).
> 
> Your interpretation of the timestamps is flawed.
> 
> The message header contains teh timestamp the servre generated teh
> message.
> The 'date' tool produces the timestamp at teh time the transaction
> delivering it was completed.
> 
> All that is evident is that the transaction took ~5 seconds from
> message
> generation to completion of delivery. That may contain any amount of
> +N
> or -N difference in the three machines clocks (server, proxy, and
> client).

I showed the output of 'date' tool to confirm that Squid received fresh
object. The client and Squid ran on the same machine.

Garri