So it's definitely not related to Vary, there's no such header in requests I tried. Also this issue affects squid even with 1 worker if shared memory is forced to on.
Interesting thing I noticed is that according to log file a lot of images are actually cached in memory but sound files are not (mp3/wav). It's not like it makes any sense but how about random example url:
squid 4, 2 workers, shared cache, no disk cache – MEM_HIT
squid 3, same config – MISS every time
squid 3, no shared cache – MEM_HIT
Could you do a brief test with this URL may be and confirm that I'm not the only one who see this issue?
On Tue, Jan 16, 2018 at 6:25 AM, Alex Rousskov <rousskov@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
On 01/15/2018 09:25 PM, Ivan Larionov wrote:
> My total hit ratio decreased in ~2 times from 40% to 20%
> 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%.
>
> > And disk cache hit ratio went up from 15-50% to stable 60-65%.
The combination of the three statements above may be a sign of a problem
unrelated to Vary: Since the disk cache can cache everything the memory
cache can and is typically much larger than the memory cache, the
incapacitation of a memory cache (due to Vary) should not have a
significant effect on overall hit ratio. It should only affect hit
response time.
The only known culprit I can think of in this context are hits for
being-cached objects: Rock lacks code that allows Squid to read
being-written objects. The shared memory cache has that code already. If
your workload has a lot of cases where clients request a being-written
object, then the overall hit ratio should go down after the memory cache
incapacitation (due to Vary).
I suspect something else is in play here though, especially if you see a
different picture with Squid v4 -- the known problem discussed above is
present in all Squid versions. I second Amos's recommendation to focus
on v4 because it is unlikely that any complicated problems are going to
be fixed in v3, even if you triage them well.
HTH,
Alex.
With best regards, Ivan Larionov.
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