[squid-users] Object Hit/Byte Hit accounting with Multiple Instances

Hello List,

I have server running 3 instances of squid-3.0.STABLE19 using a
configuration similar to that documented at http://wiki.squid-cache.org/MultipleInstances
. Each instance has all other instance configured as siblings using
the "proxy-only" directive to allow sharing of cache without
duplicating objects. This setup is working very well and has
increased server performance by over 50%.

I'm now trying to get an accurate indication of byte savings I'm
achieving with this configuration however I'm not sure that the
calculations I'm using are giving the correct results. Because each
instance maintains a separate cache_dir this seems to be a little
difficult to calculate. When instance 1 records a request as a MISS
it may in fact be a HIT (from an entire system point of view) if the
object is retrieved from the cache of instance 2 or 3.

Using a combination of "squidclient mgr:counters" and SNMP, I grab
counter values from each instance, tally and use the following formula
to calculate the byte hit ratio:

(mgr:counters:client_http.hit_kbytes_out +
snmp:cacheClientHTTPHitKb.sibling_addresses) /
(mgr:counters:client_http.kbytes_out -
snmp:cacheClientHTTPHitKb.sibling_addresses) * 100 = % cache byte hit
ratio

Using this formula, I always seem to get inconsistencies between what
squid reports and what my benchmarking tool reports (web-polygraph).
In the few cases I've checked so far, squid is always reporting a 4-5%
less byte hit than what web-polygraph reports.

Can anyone suggest a better formula to calculate byte hits from a
multi-instance configuration?

Cheers

Mick
Received on Wed Dec 15 2010 - 01:38:23 MST