[SURBL-Discuss] Combined SURBL A record format (Was: Re:BillStearns' sa-blacklistavailable as SURBL: ws.surbl.org)

Simon Byrnand simon at igrin.co.nz
Wed Apr 21 23:13:44 CEST 2004


> On Wednesday, April 21, 2004, 2:01:16 AM, Scott Truman wrote:
>> I would have thought that a bit masked record was faster, as
>> you already have all the data you need with the first call.
>> From then on bitwise CPU operations would be umpteen times
>> faster than
>> performing slower DNS callouts, even if they are cached. I am
>> assuming, however, that perhaps the Spamassassin code 'caches'
>> the first A record lookup for bitwise operations...I am not too
>> familiar
>> with the eval-rbl workings. It may be that it performs
>> subsequent DNS lookups in either case? The only way to speed
>> that up would be to load the first lookup into a variable for
>> use in later
>> bitwise calculations...
>
> Yes, you're right bitwise operations should be really fast.
>
> I suppose the only downside is readability, but Sidney makes
> some interesting arguments against that.

Does the bitwise approach only allow use of the last octet of the ip
address ? If so, that would limit you to a maximum of 8 merged "sources"
of matches that could be distinguised. Probably not a problem in practice,
but still a theoretical downside.

On the other hand, assuming that more than the last 8 bits could be used,
a reasonably large number of sources would be a lot more compact with the
bitwise approach, although it would place a definite limit on the maximum
number...

Regards,
Simon



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