[Varnish] #584: Backend probing half-close issue

Varnish varnish-bugs at projects.linpro.no
Thu Nov 19 12:34:48 CET 2009

#584: Backend probing half-close issue
 Reporter:  phk       |       Owner:  phk  
     Type:  defect    |      Status:  new  
 Priority:  normal    |   Milestone:       
Component:  varnishd  |     Version:  trunk
 Severity:  normal    |    Keywords:       
 There seems to be no clear answer to when/if it is allowed to half-close a
 TCP connection when doing a request:  After the request is sent or after
 the response has been received.

 Good cases can be made for both scenarios, but the first fails on some
 backends, whereas the second works on all.

 The varnish backend probe uses the first method, in an attemt to be able
 to figure out if the backend has ACK'ed the request or not.

 Given that the request is almost guaranteed to fit inside the first
 window, only very deficient TCP stacks will not ACK the request
 unconditionally, so this test is worthless.

 We should switch to the second method, and do a full close, after the poll
 response has been received.

Ticket URL: <http://varnish.projects.linpro.no/ticket/584>
Varnish <http://varnish.projects.linpro.no/>
The Varnish HTTP Accelerator

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