I
understand perfectly. However - I changed version of
the proxy and everywhere at the same
time changed the
headlines? Now I will return the version
3.4 and everything
will be as it was. I already did.
That's
why I ask the question - what has changed
so much that
the same configuration
I get 10 times
smaller cache hit.
26.10.15 16:29, Eliezer Croitoru пишет:
Hey
Yuri,
What have you tried until now to understand the situation of the
issue?
From your basic question I was sure that you ran some tests on
some well defined objects.
To asses the state of squid you would need some static objects and
some changing objects.
You would also be required to test using a simple UA like a
script\wget\curl and using a fully fledged UA such as
chrome\firefox\explorer\opera\safari.
I can try to give you couple cache friendly sites which will show
you what the basic status of squid.
In the past someone here asked how to cache the site:
http://djmaza.info/
which by default is built using lots of static content such as
html pages, pictures and good css and also implements cache
headers nicely.
I still do not know why wordpress main pages do not have a valid
cache headers, and what I mean by that is: Is it not possible to
have a page cached for 60 seconds? how much updates can accrue in
60 seconds? would a "must-revalidate" cost that much compared to
what there is now?(maybe it does).
Another one would be https://www.yahoo.com/ which is mostly fine
with cache and define their main page with "Cache-Control:
no-store, no-cache, private, max-age=0" since it's a news page
which updates too much.
I was looking for cache testing subjects and I am still missing
couple examples\options.
Until now what have mainly used for basic test was redbot.org and
a local copy of it for testing purposes.
And while writing to you looking for test subjects I have seen
that my own web server have a question for squid.
I have an example case which gives a great example how to "break"
squid cache.
So I have my website and the main page:
http://ngtech.co.il/
https://ngtech.co.il/ (self signed certificate)
that would be cached properly by squid!
If for any reason I would remove the Last-Modified header from the
page it would become un-cachable in squid (3.5.10) with default
settings.
Accidentally I turned ON the apache option to treat html as php
using the apache configuration line:
AddType application/x-httpd-php .html .htm
Which is recommended to be used by the first google result for
"html as php".
Once you will try the next page(with this setting on):
http://ngtech.co.il/squidblocker/
https://ngtech.co.il/squidblocker/ (self signed certificate)
You will see that it is not being cached at all.
Redbot.org claims that the cache is allowed it's own freshness for
the object but squid (3.5.10) will not cache it what so ever and
no matter what I do.
When I am removing "http as php" tweak the page response with a
Last-Modified header and can be cached again.
I am unsure who is the culprit for the issue but I will ask about
it in a separated thread *if* I will get no response here.(sorry
for partially top-posting)
Eliezer
On 25/10/2015 21:29, Yuri Voinov wrote:
In a nutshell - I need no possible
explanation. I want to know - it's a
bug or so conceived?
26.10.15 1:17, Eliezer Croitoru пишет:
Hey Yuri,
I am not sure if you think that Squid version 4 with extreme
low hit
ratio is bad or not but I can understand your sight about
things.
Usually I am redirecting to this page:
http://wiki.squid-cache.org/Features/StoreID/CollisionRisks#Several_real_world_examples
But this time I can proudly say that the squid project is
doing things
the right way while it might not be understood by some.
Before you or anyone declares that there
is a low hit ratio due to
something that is missing I will try to put some sense into how
things
looks in the real world.
Small thing from a nice day of mine:
I was sitting talking with a friend of mine, a MD to be exact
and
while we were talking I was just comforting him about the
wonders of
Computers.
He was complaining on how the software
in the office moves so slow and
he needs to wait for the software to response with results. So I
hesitated a bit but then I asked him "What would have happen if
some MD
here in the office will receive the wrong content\results on a
patient
from the software? he described it to me terrified from the
question 'He
can get the wrong decision!' and then I described to him how he
is in
such a good place when he doesn't need to fear from such
scenarios.
In this same office Squid is being used
for many things and it's
crucial that besides the option to cache content the possibility
to
validate cache properly will be set right.
I do understand that there is a need for caches and sometimes
it is
crucial in order to give the application more CPU cycles or more
RAM but
sometimes the hunger for cache can consume the actual
requirement for
the content integrity and it must be re-validated from time to
time.
I have seen couple times how a cache in a DB or other levels
results
with a very bad and unwanted result while I do understand some
of the
complexity and caution that the programmers take when building
all sort
of systems with cache in them.
If you do want to understand more about the subject pick your
favorite
scripting language and just try to implement a simple object
caching.
You would then see how complex the task
can be and you can maybe then
understand why caches are not such a simple thing and specially
why
ignore-no-cache should not be used in any environment if it is
possible.
While I do advise you to not use it I would hint you and
others on
another approach to the subject.
If you are greedy and you have hunger
for cache for specific
sites\traffic and you would like to be able to benefit from
over-caching
there is a solution for that!
- You can alter\hack squid code to meet
your needs
- You can write an ICAP service that will be able to alter the
response headers so squid would think it is cachable by default.
- You can write an ECAP module that will
be able to alter the response
headers ...
- Write your own cache service with your
algorithms in it.
Take in account that the squid project tries to be as fault
tolerance
as possible due to it being a very sensitive piece of software
in very
big production systems.
Squid doesn't try to meet the
requirement of "Maximum Cache" and it is
not squid that as a caching proxy makes a reduction of any cache
percentage!
The reason that the content is not
cachable is due to all these
application that describe their content as not cachable!
For a second of sanity from the the
squid project, try to contact
google\youtube admins\support\operators\forces\what-ever to
understand
how would you be able to benefit from a local cache.
If and when you do manage to contact
them let them know I was looking
for a contact and I never managed to find one of these available
to me
on the phone or email. You cannot say anything like that on the
squid
project, the squid project can be contacted using an email and
if
required you can get a hold of the man behind the software(while
he is a
human).
And I will try to write it in a geeky way:
deny_info 302:https://support.google.com/youtube/
big_system_that_doesnt_want_to_be_cached
Eliezer
* P.S If you do want to write an ICAP service or an ECAP
module to
replace the "ignore-no-cache" I can give you some code that will
might
help you as a starter.
On 25/10/2015 17:17, Yuri Voinov wrote:
Hi gents,
Pay attention to whether someone from the test SQUID 4 as
extremely low
of cache hits from the new version? Particularly with respect
to sites
HTTPS directive "no cache"? After replacing the Squid 3.4 to 4
squid
cache hit collapsed from 85 percent or more on the level of
5-15
percent. I believe this is due to the exclusion of support
guidelines
ignore-no-cache, which eliminates the possibility of
aggressive caching
and reduces the value of caching proxy to almost zero.
This HTTP caches normally. However, due to the widespread use
of HTTPS
trends - caching dramatically decreased to unacceptable
levels.
Noticed there anyone else this effect? And what is now with
caching?
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