Retry backend fetches one time if we got a recycled conncetion and

the transfer failed before we received anything.

Fixes: #749



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@5102 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/cache_center.c

@@ -439,6 +439,15 @@ cnt_fetch(struct sess *sp)
 	http_Setup(sp->wrk->beresp, sp->wrk->ws);
 
 	i = FetchHdr(sp);
+	/*
+	 * If we recycle a backend connection, there is a finite chance
+	 * that the backend closed it before we get a request to it.
+	 * Do a single retry in that case.
+	 */
+	if (i == 1) {
+		VSC_main->backend_retry++;
+		i = FetchHdr(sp);
+	}
 
 	/*
 	 * Save a copy before it might get mangled in VCL.  When it comes to

include/vsc_fields.h

@@ -55,6 +55,7 @@ VSC_F_MAIN(backend_reuse,	uint64_t, 0, 'a', "Backend conn. reuses")
 VSC_F_MAIN(backend_toolate,	uint64_t, 0, 'a', "Backend conn. was closed")
 VSC_F_MAIN(backend_recycle,	uint64_t, 0, 'a', "Backend conn. recycles")
 VSC_F_MAIN(backend_unused,	uint64_t, 0, 'a', "Backend conn. unused")
+VSC_F_MAIN(backend_retry,	uint64_t, 0, 'a', "Backend conn. retry")
 
 VSC_F_MAIN(fetch_head,		uint64_t, 1, 'a', "Fetch head")
 VSC_F_MAIN(fetch_length,	uint64_t, 1, 'a', "Fetch with Length")