[squid-users] cache hit rate isn't what I'd expect

Thu Sep 28 22:29:49 UTC 2017

So this grep through my access logs for this single URL does a good
job illustrating a rather interesting problem:

$ grep -h 'https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr
text/css ip_index=0,client=m0078269' access.*.log | sort

26/Sep/2017:20:10:27 TCP_HIT/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:10:33 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:10:42 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:10:47 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:10:52 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:10:56 TCP_HIT/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:11:11 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:11:15 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:11:19 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:11:24 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:11:28 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:11:32 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:11:37 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:11:41 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:11:48 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:11:53 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:11:57 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:12:01 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:12:06 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:12:10 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:12:14 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:12:19 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:12:23 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:12:28 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:12:32 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:12:37 TCP_HIT/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:12:41 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:12:49 TCP_HIT/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:12:59 TCP_HIT/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:13:03 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:13:08 TCP_HIT/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:13:13 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:13:27 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:13:33 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:13:37 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:13:42 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:13:47 TCP_HIT/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:13:52 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:13:56 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:14:00 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:14:06 TCP_HIT/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:14:36 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:14:41 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:14:45 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094
26/Sep/2017:20:14:54 TCP_MISS/200
https://static.licdn.com/sc/h/ddzuq7qeny6qn0ysh3hj6pzmr text/css
ip_index=0,client=m0078269_9094

At first I thought this was because the because I have a bunch of
clients, each of which behaves exactly the same except for one thing:
the client includes a unique request header that squid strips off
before forwarding to the server (you can see it logged as
client=mXXXXX_XXXX).  But in this case I've controlled for that and
only grep'd for a single client's request.  I've even tried setting
"vary_ignore_expire on", but that doesn't seem to be a complete fix.

I can't for the life of me understand why the low hit rate though.

--
Aaron Turner
https://synfin.net/         Twitter: @synfinatic
My father once told me that respect for the truth comes close to being
the basis for all morality.  "Something cannot emerge from nothing,"
he said.  This is profound thinking if you understand how unstable
"the truth" can be.  -- Frank Herbert, Dune