Varnish Performance Issue

[Paras Fadte]

Hi,

I am faced with following performace issue with respect to Varnish.

Load on Varnish increases suddenly at times. When this happens ,
"varnishhist" shows a high number of misses and the cache hit ratio
decreases and the response time  increases. Also there is a gradual
increase in the number of "overflowed work requests" over a period of
time. I have attached mrtg of CPU utilisation for perusal. It shows a
very spiky graph.

What could be the issue ? What parameters do  I need to adjust to
overcome this load issue ?

 The settings used are :

lru_interval = 30
thread_pool_max = 750 (initially I had set this to 300 but the load
issue was the same)
overflow_max   = 100000
sess_timeout  =  2
listen_depth  =  4096

Cache size is 3GB ( ramdisk)
Varnish Version:2.0.2 (built from source)
OS:SUSE LINUX 10.1 (X86-64)
RAM:20GB
CPU: Intel(R) Xeon(R) CPU   E5430  @ 2.66GHz

Thanks in Advance.

-Paras
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