High delay between accept'd and processing

[Cosimo Streppone]

On Fri, 23 Nov 2012 10:57:20 +0100, <Jonathan.Huot at thomsonreuters.com>  
wrote:

> We're doing some tests with Varnish, and I'm trying to understand some  
> timings.

Just thinking out loud...
Please correct me where I'm wrong.

If:
1) you are sending a request that hashes to the same object  &&
2) your backend is taking a long time to answer              &&
3) the object is not in cache when the first request hits

then it could be that varnish is "herding", waiting for the backend
to respond before satisfying all the requests at once.

You should see "Herd(?:ing)" in the varnishlog output.

However:

> With a very low traffic (<5 req/sec), I got sometime a delay
> of several *seconds* in the fourth number of ReqEnd [1].

The 4th number is time from the session start, so
if your client is using KeepAlive, it could well be that
it connects at t0 and sends n requests where the nth request
starts at t0 + 5s.

Or could be a mix of keepalive + herding?

-- 
Cosimo