Sporadic "backend write error: 11" errors

[HC Saustrup]

On 7/30/10 4:43 PM, HC Saustrup wrote:
>
>    46 FetchError   c backend write error: 11 <-- oops!
Error 11 seems to be "Resource temporarily unavailable."

I'm grasping at straws here, but could this error show up if the client 
closed the connection before the request was answered by the backend?

I tried dumping a request that failed with tcpdump and wrote a script to 
run 20 concurrent requests like it to the backend, but all respond with 
correct data and code 200 (3000-16000ms/request - way over the 5000ms 
where most of the sporadic 503's happen). I simply can't get it to fail 
myself, neither by script or via the browser. I get plenty errors in 
varnishlog still, though :-(

Any clues?

Cheers,
HC