varnishd restarting randomly

[glenn at mp3lyrics.org]

We've been running varnish on www.mp3lyrics.com for many years,
there has been a problem with varnish restarting at random intervals.
Some times varnish can work for several days before it automatically
restarts (but its rare), and some times it restarts up to 10 times per
day (more "normal").
It does not seem to have anything to do with traffic amount.
This is starting to get annoying and we've reached the point where we
want to either fix the problem with varnish or get another cache
machine.
Last night varnish didn't restart, but it seems it kind of froze. It
didn't fetch data from the webserver, and didn't respond to
http-requsts from the net (this is the first time I've experienced a
varnish freeze like this)
When it froze, all I had to do was to manually restart it, then it
started running "normally" again.

I am unsure whether varnish responds slowly to http-requests from the
net during the automatic restarts or not, but I have come across
situations when varnish is starting to respond slowly, then I restart
it and it starts responding quick again.
This behavior seems totally random, but I have noticed that varnish
can seem slow when very many url.purge commands have been sent to it.
However, the automatic restarting does not seem to have anything to do
with the amount of url.purges sent to varnish (but I can be wrong).

mp3lyrics is a fairly big site, it has several millions (cacheable)
pages, about 200.000 unique users per day, about 300.000 pageviews,
and about 4mill varnish requests per day.
The server is in no way overloaded, apache alone is very capable of
handling the requests, but a cache machine is off course wanted anyway
if it works correctly.
Currently varnish has been given 16GB of ram, I've tried with
different amounts, but the problem seems to be the same.

I need some help to figure out where to start looking for the reason to this.
If someone could tell me what kind of server type / configuration and
varnish stats / configuration data is needed to start searching for
the reason I'll be happy to provide it.

(or should this request go to the varnish-bugs mailinglist?)

- Glenn-Erik Sandbakken