[master] a3fcdabb9 Comment on #2951

[Nils Goroll]

commit a3fcdabb9d0d303998642fcde315b2a189e84d1b
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Mon Apr 15 16:01:18 2019 +0200

    Comment on #2951

diff --git a/bin/varnishd/cache/cache_fetch.c b/bin/varnishd/cache/cache_fetch.c
index a7ecafa22..82af410e2 100644
--- a/bin/varnishd/cache/cache_fetch.c
+++ b/bin/varnishd/cache/cache_fetch.c
@@ -674,6 +674,19 @@ vbf_stp_condfetch(struct worker *wrk, struct busyobj *bo)
 
 /*--------------------------------------------------------------------
  * Create synth object
+ *
+ * replaces a stale object unless
+ * - abandoning the bereq or
+ * - leaving vcl_backend_error with return (deliver) and beresp.ttl == 0s or
+ * - there is a waitinglist on this object because in this case the default ttl
+ *   would be 1s, so we might be looking at the same case as the previous
+ *
+ * We do want the stale replacement to avoid an object pileup with short ttl and
+ * long grace/keep, yet there could exist cases where a cache object is
+ * deliberately created to momentarily override a stale object.
+ *
+ * If this case exists, we should add a vcl veto (e.g. beresp.replace_stale with
+ * default true)
  */
 
 static enum fetch_step