Connections dropped under load

[George Georgovassilis]

Hello all,

I'm having trouble with dropped connections under a loadtest.

The setup: Java app with Tomcat 6 under an Ubuntu 8.04 VPS (virtual 
linux server) proxied with a varnish 2.1.2 (16M malloc)

The test: The load test itself is aimed at generating many HTTP 
connections, which after a brief setup phase are served entirely by 
varnish. Hence the system load remains low (2% CPU consumed by varnish 
at 300 requests / second).

The problem: As a measure for response, I am requesting an image from 
the webapp running in Tomcat while the loadtest is underway. However 
that either times out or is delivered after several seconds. Varnishlog 
will often either not show the request (RxURL) at all, or show it 
several seconds after the browser dispatched it.

I don't believe it to be a network/OS issue, as the server will happily 
accept SSH connections while the loadtest is ongoing and remains 
responsive throughout the test.

How do I debug this?

Thanks in advance,
G.

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