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TIMEOUT_ROUNDROBIN_PARENT and poor SIBLING_HIT performance

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Hi,

I've 2 problems where squid is taking excessive time to service a request.

My setup:
-Accelerator setup
-backends are on load balancer, squid is configured to connect to the load balancer IP multiple times
-squid's configured to store the cache as long as possible.
-icp time is set to really high, otherwise some siblings doesn't respond in time. Should this be lowered?

Version:
Squid Cache: Version 2.7.STABLE9
configure options: '--prefix=/apps/squid' '--enable-x-accelerator-vary' '--enable-linux-netfilter' '--enable-cache-digests' '--enable-htcp' '--enable-snmp' '--enable-referer-log' '--enable-useragent-log' '--enable-delay-pools' '--enable-icmp' '--enable-async-io=500' '--with-maxfd=10240' '--enable-removal-policies=lru,heap' '--enable-follow-x-forwarded-for' '--enable-epoll' '--with-large-files'

Relevant config:

http_port 80 vhost defaultsite=cache.example.com
cache_mem 512 MB

cache_peer lb.example.com parent 80 0 round-robin no-query originserver no-netdb-exchange no-digest name=lb_01

... <snip>

cache_peer lb.example.com parent 80 0 round-robin no-query originserver no-netdb-exchange no-digest name=lb_10

cache_peer cache01.example.com sibling 80 3130 proxy-only no-delay allow-miss weight=1 no-netdb-exchange no-digest name=cache01

..<snip>

cache_peer cache08.example.com sibling 80 3130 proxy-only no-delay allow-miss weight=1 no-netdb-exchange no-digest name=cache08

client_persistent_connections off
server_persistent_connections off
digest_generation off

icp_access allow all
icp_hit_stale on
icp_query_timeout 7000
maximum_icp_query_timeout 10000
nonhierarchical_direct off
url_rewrite_host_header off

offline_mode on
--------------------------------------

TIMEOUT_ROUNDROBIN_PARENT

All the TIMEOUT requests took at least 7000 ms, which is the value of icp_query_timeout. Some requests took at over 30 sec to complete. I crossed referenced those long requests against the backends and notice a big mismatch in the times. The backends are tomcat apps w/ Java 1.6. I extracted the times from the tomcat access log.

Squid Time    Backend time:
7922            924
8422            1421
7488            487
12835           5833
25098           18096
34793            611
21806            14804

------------------------------------
High SIBLING_HIT response time:

The same problem occurs with sibling hits. The logged process time on the sibling and the one requesting from the sibling vastly differs:

Squid Time    Time on Sibling's Log
4534            30
23994           12959
6661            40

---------------
Does anyone know of a reason why it would take so long for squid to complete a request??

mike


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