Re: [squid-users] squid cache TCP_REFRESH_MODIFIED

On 20/02/2012 6:21 p.m., parashuram wrote:
> On 2/18/2012 10:02 AM, Amos Jeffries wrote:
>> On 18/02/2012 12:26 a.m., parashuram wrote:
>>> Hi all,
>>> I am using squid to cache dynamic responses from my particular server
>>>
>>> everything working fine,
>>> When I make first request access.log has
>>> 1329473470.110 0 192.168.0.40 TCP_MISS/200 856 GET
>>> http://[ipv6address]:8080/.well-known/core - DIRECT/::1 text/html
>>>
>>> Next request it logs following
>>> 1329473479.050 0 192.168.0.40 TCP_REFRESH_MODIFIED/200 856 GET
>>> http://[ipv6address]:8080/.well-known/core - DIRECT/::1 text/html
>>>
>>> request is in cache but due to resources being changed response is
>>> from origin server( I've ignored must revalidated in refresh
>>> pattern). I wanted request should be served from cache even if its
>>> modified and log TCP_HIT or TCP_MEM_HIT in access.log.
>>> any idea what might be going wrong??? suggestion how to tell squid
>>> not send revalidiate signal to origin server to cross check for
>>> resource modification???
>>>
>>> server header response is as follows
>>>
>>> (Status-Line) HTTP/1.0 200 OK
>>> Date Fri, 17 Feb 2012 10:11:19 GMT
>>> Content-Type text/html
>>> Last-Modified Wed, 15 Feb 2012 07:48:34 GMT
>>> Accept-Ranges bytes
>>> Content-Lenght 8334
>>> Cache-Control max-age=86400,public
>>
>> Notice how "must-revalidate" is not present. Your override turing it
>> off does nothing.
>>
>> What is happening here is that max-age is specifying that the object
>> is stale when older than 1 day, and needs revalidatating. (Date minus
>> Last-Modified) is stating that it is currently 2 days old.
> Thanks for reply, Now current Header is a follows
>
> (Status-Line) HTTP/1.0 200 OK
> Date Mon, 20 Feb 2012 04:39:10 GMT
> Content-Type text/html
> Last-Modified Mon ,20 Feb 2012 04:29:10 GMT
> Accept-Ranges bytes
> Content-Lenght 8334
> Cache-Control max-age=86400,public
> Expires Tue, 21 Feb 2012 04:29:10 GMT
> X-Cache MISS from colinux
> Via 1.0 colinux (squid/3.1.18)
> Connection close
>
> But still it logs as TCP_REFRESH_MODIFIED for my server, but other web
> pages (i.e www.squid-cache.org ) showing TCP_MEM_HIT with same
> response header.

Servers such as squid-cache.org respond with a 304 (Not Modified) status
to If-Modified-Since requests when the requested object has not changed.
Allowing Squid to serve its cached copy (HIT).

The reason you are getting "MODIFIED" is that the server is sending back
a 2xx status with new data.

>> Squid is only performing a REFRESH (if-modified-since) check, this is
>> very efficient if the server supports
> Is it possible to disable REFRESH(if-modified-since) check. ?? if so
> how??

You either remove the max-age control and depend on Expires alone. Or
extend max-age to be current age of the object + 86400 seconds each time
a response is sent.

The bigger problem is that the server is sending 200 instead of 304. You
can extend the max-age and/or expires value using 304 responses with no
body.

Fix that and you will both save bandwidth and get something saying
*REFRESH_HIT or *_REFRESH_UNMODIFIED (which is the same thing even if
the letters "HIT" are not part of the label).

Amos
Received on Mon Feb 20 2012 - 08:11:03 MST