cache empties itself?

[Sascha Ottolski]

Am Freitag 04 April 2008 04:37:44 schrieb Ricardo Newbery:
>           sub vcl_fetch {
>               if (obj.ttl < 120s) {
>                   set obj.ttl = 120s;
>               }
>           }
>
> Or you can invent your own header... let's call it  X-Varnish-1day
>
>           sub vcl_fetch {
>               if (obj.http.X-Varnish-1day) {
>                   set obj.ttl = 86400s;
>               }
>           }

so it seems like I'm on the right track, thanks for clarifying. now, is 
the ttl a information local to varnish, or will it set headers also (if 
I look into the headers of my varnishs' responses, it doesn't appear 
so)?

what really confuses me: the man pages state a little different 
semantics for default_ttl. in man varnishd:

     -t ttl      Specifies a hard minimum time to live for cached
                 documents.  This is a shortcut for specifying the
                 default_ttl run-time parameter.

     default_ttl
           The default time-to-live assigned to objects if neither
           the backend nor the configuration assign one.  Note
           that changes to this parameter are not applied retroac‐
           tively.

           The default is 120 seconds.


"hard minimum" sounds to me as if it would overwrite any setting the 
backend has given. however, in man vcl it's explained, that default_ttl 
does only affect documents without backend given TTL:

     The following snippet demonstrates how to force a minimum TTL
     for all documents.  Note that this is not the same as setting
     the default_ttl run-time parameter, as that only affects doc‐
     ument for which the backend did not specify a TTL.

         sub vcl_fetch {
             if (obj.ttl < 120s) {
                 set obj.ttl = 120s;
             }
         }


the examples have a unit (s) appended, as in the example of the man 
page, that suggests that I could also append things like m, h, d (for 
minutes, hours, days)?

BTW, in the trunk version, the examples for a backend definition have 
still the old syntax.

         backend www {
             set backend.host = "www.example.com";
             set backend.port = "80";
         }


instead

         backend www {
             .host = "www.example.com";
             .port = "80";
         }


Thanks a lot,

Sascha