[rbldnsd] regular expression support for rbldnsd

[Steven Champeon]

on Wed, Aug 12, 2009 at 02:45:51PM -0400, Jon Lewis wrote:
> On Wed, 12 Aug 2009, Per Jessen wrote:
>
>> Interesting idea.  We have a list of such patterns which is evaluated by
>> Postfix.  I can't immediately see if a DNS-based solution instead would
>> improve things.
>
> The benefit is centralized management of the regex's and a plug-in standard 
> (DNSBL query) that just about everything supports.

I'd wager that our regex processing library is faster than Postfix's;
it's based on the idea that the string being matched against is a
hostname and so the regexes are searched according to the TLD, then SLD,
then domain, only then are any regexes checked against the string.

As I recall, Postfix uses a simple brute-force "check all patterns until
something matches" approach. Depending on the size and coverage of the
patterns file (ours is over 41K patterns in 23K domains), this would
probably represent a pretty severe performance hit. The library also
lowercases all queries, to avoid the overhead of a case-insensitive
regex scan.

Steve

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