[squid-users] Queue incoming requests when fetching from origin

[Jaap Dam]

Hi,

I've got a reliable but slow backend that sends cacheble responses. When I
run a manual test, I can see I miss the cache every one in a while and got
hits most of the time. This is also reflected in the response time, 200+ ms
for a miss, ~20ms for a hit.

However when I request the same resource multiple times at the same
instant, I see multiple requests at the origin server. Ideally I would like
to have only a single request to the origin server and queuing all other
incoming requests in Squid.

The 'collapsed_forwarding on' option seems to do exactly as I want, however
when I turned this option and restarted Squid I still see multiple requests
at the backend.

I've tried to add a cache_dir as suggested in section 'Known issues and
shortcomings' on  http://wiki.squid-cache.org/Features/CollapsedForwarding but
to no avail.

I've placed the config directive on multiple locations in the configuration
file, both before and after the http_port directive as well as the
cache_dir directive. Again no results.

Is the collapsed_forwarding directive the correct one to use for my
use-case or am i missing something?

I'm using the default configuration of version 3.5.19 with the following
changes:

#Queue incoming requests when a request is send to the backend. I.E.
collapse request into a single backend request.
collapsed_forwarding on

# Squid normally listens to port 3128
http_port 3128 accel no-vhost defaultsite=localhost ignore-cc

#Backend requires basic auth
cache_peer 127.0.0.1 parent 53142 0 no-query originserver name=myAccel
login=username:password

#Allow caching of files that have a ttl of 1 seconds
minimum_expiry_time 1 seconds

acl our_sites dstdomain localhost
http_access allow our_sites
cache_peer_access myAccel allow our_sites
cache_peer_access myAccel deny all

See also:
http://serverfault.com/questions/782877/on-multiple-request-to-squid-send-a-single-request-to-a-backend-and-queue-other
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