[squid-users] squid doesn't cache objects in memory when using SMP and shared memory cache

[Alex Rousskov]

On 01/15/2018 09:25 PM, Ivan Larionov wrote:

> looks like caching works as expected in squid 4 so it'll be better
> solution than messing up with headers probably.

FYI: Vary caching in shared memory is not supported in any Squid
version, including v4.

Alex.


> On Mon, Jan 15, 2018 at 10:26 AM, Alex Rousskov wrote:
> 
>     On 01/14/2018 10:53 PM, Ivan Larionov wrote:
> 
>     > After migrating squid from non-SMP/aufs to SMP/rock memory cache hit
>     > ratio dropped significantly. Like from 50-100% to 1-5%.
> 
>     This could be a side effect of not supporting Vary caching in shared
>     memory: https://bugs.squid-cache.org/show_bug.cgi?id=3806#c9
>     <https://bugs.squid-cache.org/show_bug.cgi?id=3806#c9>
> 
> 
>     > And disk cache hit ratio went up from 15-50% to stable 60-65%.
> 
>     I hope your total/combined hit ratio improved overall.
> 
> 
>     > it looks like in SMP/rock mode squid avoids using memory for small
>     > files like 1-3KB but uses it for 10KB+ files.
> 
>     No, there is no such size-discrimination code in Squid.
> 
> 
>     > I started tracking down the issue with disabling disk cache completely
>     > and it didn't change anything, I just started to get MISS every time for
>     > the URL which was getting MEM_HIT with an old configuration. Then I
>     > changed "workers 2" to "workers 1" and started getting memory hits as
>     > before.
> 
>     For a clean apples-to-apples test, make sure you use
>     "memory_cache_shared on" when using a single worker without rock
>     cache_dirs.
> 
> 
>     > Am I doing anything wrong? Which debug options should I enable to
>     > provide more information if it seems like a bug?
> 
> 
>     Vary caching should be fixed as well, of course, but perhaps there is
>     another problem we do not know about. I would start by eliminating Vary
>     as the known problem. When using a test transaction, make sure the
>     response does not have a Vary header. Or configure Squid to log the Vary
>     header and remove the corresponding transactions when computing
>     adjusted-for-Vary memory cache hit ratio.
> 
> 
>     HTH,
> 
>     Alex.
> 
> 
> 
> 
> -- 
> With best regards, Ivan Larionov.