Re: TXT Records

I think that the performance of the reference implementation of SPF is 
important. This leads me to wonder if we should perform some set of the 
DNS lookups and mechanism evaluations in parallel. For example:
   Extract the ordered list of mechanisms.
   While list not empty do
      extract initial subset whose 'result's are the same   (i.e. get 
the list of '+' from the front)
      initiate DNS lookups in parallel
      while pending lookups do
            get result
            if mechanism matches, then return result.
       done
    done

There are various complications associated with include and redirect, 
but I'm sure that these can be handled.
Note that this works nicely for cases like:

      v=spf1 a mx ptr:%{d2} -all

It *may* initiate more lookups than necessary, but the latency will 
(almost certainly) be lower. Of course, you could just perform all the 
lookups and then evaluate until you get an answer -- but that is even 
more complex.
If the reference implementation goes to these lengths, then it will 
eliminate a criticism that the specification is inherently unusable for 
performance reasons.
It *may* also be that the spec needs to note that mechanisms may be 
evaluated out of order, but the overall result of an SPF check is as 
though the mechanisms were evaluated from left to right. The reason that 
this makes a difference is that you might have a complex SPF record that 
triggered DNS lookups that had side effects (e.g. recorded an entry into 
a log file).
Just my late night ramblings....

Philip

Jonathan Steinert wrote:

> I need to just point out; If we keep adding things to do in DNS 
> lookups in a serial order, the time it takes to do an SPF lookup goes 
> up and up and up.
> I'm not saying that these aren't good ideas, but we need to realize 
> that  the tradeoff is in longer SPF lookup times. The trouble is that 
> SPF is being designed to be fast enough to run at message acceptance 
> time, and on high load servers it's bad to keep a connection open for 
> long.
> --Jonathan

--
Philip Gladstone
* Check out the live pondcam at http://pond.gladstonefamily.net

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