On Mon, Oct 4, 2010 at 10:34 AM, Nils Goroll <= >span dir=3D"ltr"><slink at schokola.de= >> wrote:
> >

r-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Hi,
>
>I've had a first discussion with phk on IRC. IIUC, his main concern was= > that
>introducing the new states & VCL procedures would increase complexity a= >nd raise
>the entry barrier, in particular with regard to users wanting to (easily)r> >customize the default vcl.
>
>I will elaborate on the reasons for the proposed solution.
>
>a) vcl_stale()
>--------------
>
>The alternative we've discussed on IRC is to fall into vcl_miss(): If a= >n obj
>eligible for refresh was found, default backend conditional request headers= > were
>added to bereq, and vcl_miss() would see obj. It wouldn't for the curre= >nt case
>(a real miss). To avoid a backend conditional request, admins could remove = >the
>conditional headers (If-...) from bereq. return(refresh) wouldn't exist= >.
>
>Here's my subjective perspective on why vcl_stale() would make sense:r> >
>- Without vcl_stale(), the semantics of vcl_miss() would mean "I have = >not found
> =A0an object eligible for delivery, but might have found one for refresh&q= >uot;, which
> =A0I believe will confuse users more than help.
>
> =A0Mostly, this does open up a whole lot of oddities and questions:
>
> =A0- vcl_miss would see obj only if it was a "stale miss"
>
> =A0 =A0Odd: What would obj.status return for a "real miss"?
>
> =A0- cnt_miss could prepare bereq.http.If-... headers only if it was a &qu= >ot;stale
> =A0 =A0miss"
>
> =A0- We would be able to return (deliver) for a "stale miss", bu= >t not for a real
> =A0 =A0miss: What do we do here? We can't decide on the correctness of= > the VCL
> =A0 =A0at compile time. Would return (deliver) fall back to a return (fetc= >h)
> =A0 =A0is it's a "real miss"?
>
>- Users would need to put more conditionals into vcl_miss for special handl= >ing
> =A0of "stale" cases, =E0 la:
>
> =A0if (obj) {
> =A0 =A0 =A0 =A0# do stale case handling
> =A0} else {
> =A0 =A0 =A0 =A0# existing code
> =A0}
>
>Depending on whether we want to default to the new or current behavior, ar> >default vcl_stale() would look like:
>
>vcl_stale() {
> =A0 =A0 =A0 =A0return (refresh);
>}
>
>or
>
>vcl_stale() {
> =A0 =A0 =A0 =A0call vcl_miss;
>}
>
>
>
>If we put the mechanics into vcl_miss, retaining current behavior would nee= >d
>something like this with a full backend conditional:
>
>vcl_miss() {
> =A0 =A0 =A0 =A0if (obj) {
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0unset bereq.http.If-Match;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0unset bereq.http.If-Modified-Since;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0unset bereq.http.If-None-Match;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0unset bereq.http.If-Range;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0unset bereq.http.If-Unmodified-Since;
> =A0 =A0 =A0 =A0}
>}
>
>
>My personal impression is that vcl_stale would help retain clarity rather t= >han
>complicate things, in particular because it would help to limit additional<= >br> >processing to the cases when it's actually needed.
>
>b) vcl_refresh()
>----------------
>
>The alternative to vcl_refresh() would be to put additional logic into vcl_= >fetch().
>
>Similar to the stale case, we would want to have access to the original obj= >ect
>in the cache and the beresp from the refresh, so obj would be available onl= >y if
>vcl_refresh was entered with (beresp.status =3D=3D 304).
>
>
>
>We really want to retain clarity and not introduce unneeded additional
>complexity. I believe that introducing more VCL states and procedures would= > help
>to achieve this, in particular because the preconditions for each case were= >
>clear and visibility of a cache object was well defined.
>
>Thanks, Nils
>
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