2.7 STABLE 9 responds very slowly or stops responding

["TJM" <powiadomienia@xxxxxxxxxxxxxxxx>]

Hello,

For last 3 days I had weird problems with Squid 2.7 stable 
9.
I'm running that version since it was released and it 
worked just fine for these few months.

Then suddenly users behind the proxy started to report 
serious slowdowns or downtimes.

This is a very low volume proxy with less than 30 users, 
set-up mostly to save bandwidth during peak hours.
I'm using it myself everyday, so when the last slowdown 
started I was able to look at the logs almost immediately.

When the slowdown event starts, usually the proxy almost 
stops responding - for example, if I open new tab in a 
brower and enter URL, it might take several minutes until 
it starts loading and then it might take another couple of 
minutes since the page loads completely (if it does at 
all).
It lasts for a while, sometimes it will just go away 
without restarting the proxy, sometimes not.
During the slowdown, any requests made do not appear in 
the access log until the squid handles the request, which 
as I mentioned above might take several minutes.
Also, during last slowdown I've found weird log entries in 
the access.log, a sample from access log, 10.0.0.4 is the 
cache IP address:

1281379957.060 899446 10.0.0.4 TCP_MISS/504 227 POST 
http://10.0.0.4:3128/p4s - DIRECT/10.0.0.4 text/html
1281379957.060 899446 10.0.0.4 TCP_MISS/504 227 POST 
http://10.0.0.4:3128/p4s - DIRECT/10.0.0.4 text/html
1281379957.060 899445 10.0.0.4 TCP_MISS/504 227 POST 
http://10.0.0.4:3128/p4s - DIRECT/10.0.0.4 text/html
1281379957.060 899445 10.0.0.4 TCP_MISS/504 227 POST 
http://10.0.0.4:3128/p4s - DIRECT/10.0.0.4 text/html
1281379957.060 899445 10.0.0.4 TCP_MISS/504 227 POST 
http://10.0.0.4:3128/p4s - DIRECT/10.0.0.4 text/html


Also, the cache.log complains about cache running out of 
file descriptors. 
Where should I look at to find what's the cause of this 
problem ? I doubt that it's the config itself, because the 
proxy was running fine for like 7-8 years, upgraded 
everytime when stable version came out.