[PATCH] backend conditional requests 5th release

[Geoff Simmons]

Hello again,

And yet another version (v5) of the patch for conditional backend
requests. Like the last version, this is one is to keep pace with recent
commits to the trunk. The patch applies to:

commit 13c60b522a6c7abe9cc1052c2a244f25f2ba5227
Date:   Tue Mar 8 14:47:57 2011 +0100

phk committed some changes related to this feature, mainly the addition
of the new timer variable to VCL. There are also some changes in the way
that previous version of the patch worked.

- The name of the timer for conditional requests changed again, now to
"keep". The management parameter is "default_keep".

- In addition to beresp.keep, obj.keep and stale_obj.keep, there is now
req.keep, which sets an upper bound for the keep time within a session.
(Like req.ttl, which phk added yesterday.)

- The keep interval now begins after ttl and grace have elapsed, so an
object is available for conditional requests after obj.ttl + obj.grace,
and is scheduled for eviction after obj.ttl + obj.grace + obj.keep. (In
previous versions of the patch, the keep interval began after ttl
elapses, independent of grace, and object were evicted after obj.ttl +
max(obj.grace, obj.keep).)

- The default value default_keep is now 0, so you need to set a non-zero
default_keep, or set keep in VCL, to make the conditional requests happen.

The Wiki page has been updated to reflect all of this:

http://www.varnish-cache.org/trac/wiki/BackendConditionalRequests

@phk: I made one change in the commits from yesterday. Since
default_keep = 0 and EXP_get_*() was returning -1 for any timer = 0,
*.keep was always -1 unless it was changed in VCL. I think VCL authors
wouldn't expect that; I got feedback about an earlier version in which
beresp.keep was -1 after a backend validation, which both the reporter
and I thought was wrong, so I fixed it in the next version.

Now I have this in cache_expire.c:

        double                                                  \
        EXP_Get_##fld(const struct exp *e)                      \
        {                                                       \
-               return (e->fld > 0. ? e->fld : -1.);            \
+               return (e->fld > 0. ? e->fld : 0.);             \
        }                                                       \

This required a change in test case b00040.vtc, which expects req.grace
== -1, but that doesn't seem to be a critical value there.


Best,
Geoff
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