~5% of cache hits very slow

[Ben Drees <ben@xxxxxxxxxxx>]

Hi,

I'm running Squid (2.5 STABLE 12) in a reverse proxy setup, caching 
mostly dynamic content with unreadably long parameterized URLs. Most 
cache hits take about 2 - 4 milliseconds (as indicated by the access 
log), but I see frequent outliers in the 200 - 800 millisecond range. 
These seem to be mostly TCP_HIT and TCP_IMS_HIT cases, not cases where 
Squid connects with an origin server. This is on a very lightly loaded 
test server. There is no fancy authorization happening. Are there any 
well known configuration issues that could be causing this? Even if the 
hits are on disk rather than in memory, the TCP_IMS_HIT case should only 
need to consult an in-memory index structure and reply with a 304, right?

Thanks,
Ben