[Varnish] #690: Allow for a negative grace period for internal crawler

[Varnish]

#690: Allow for a negative grace period for internal crawler
------------------------+---------------------------------------------------
 Reporter:  mikeytown2  |        Type:  enhancement
   Status:  new         |    Priority:  normal     
Milestone:              |   Component:  build      
  Version:  2.0         |    Severity:  normal     
 Keywords:  grace       |  
------------------------+---------------------------------------------------
 We use an internal crawler to refresh the pages cache. So if we want
 something refreshed very soon but not deleted, this will do it. This
 allows us to almost always serve the request from the cache & still have
 content updated on a regular basis.

 vcl configuration
 {{{
    if (req.http.user-agent == "our-crawler") {
     #HACK
     C{ VRT_l_req_grace(sp, -300);  }C
    } else {
     # in case "our-crawler" hasn't refresh the data; this will reduce the
 load on the backend
       set req.grace = 5m;
    }
 }}}

 patch to cache_hash.c

 {{{
 --- ./bin/varnishd/cache_hash.c                2009-12-16
 00:45:49.000000000 -0800
 +++ ./bin/varnishd/cache_hash.c             2010-02-22 11:29:06.000000000
 -0800
 @@ -293,6 +293,15 @@
                                                 grace_o = o;
                 }

 +        if (sp->grace < 0) {
 +               sp->grace = -sp->grace;
 +          if (o != NULL) {
 +            o->ttl = sp->t_req-1;
 +            o = NULL;
 +          }
 +          grace_o = NULL;
 +        }
 +
                 /*
                  * If we have seen a busy object or the backend is
 unhealthy, and
                  * have an object in grace, use it, if req.grace is also
 --- ./bin/varnishd/cache_vrt.c    2009-10-23 01:00:09.000000000 -0700
 +++ ./bin/varnishd/cache_vrt.c 2010-02-22 11:29:35.000000000 -0800
 @@ -534,8 +534,6 @@
  {

                 CHECK_OBJ_NOTNULL(sp, SESS_MAGIC);
 -              if (a < 0)
 -                              a = 0;
                 sp->grace = a;
  }
 }}}

-- 
Ticket URL: <http://www.varnish-cache.org/ticket/690>
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