Dave Sill writes:
> Each qmail-remote does one DNS lookup, so at most concurrencyremote
The fact that qmail-remote barfs with a 'CNAME lookup failed' in certain
well-known situations leads me to believe that there are at least two DNS
lookups happening in qmail-remote: a CNAME, followed by an MX lookup. I
always thought that it was a waste, RFC 1035 guarantees that a CNAME
response will be returned, if present, in the response to any query for the
same host. There's never a need for Qmail to do an explicit CNAME query.
> DNS lookups are concurrent, and qmail doesn't have to wait for all of
> them before sending any messages.
>
> >Additionally, I'm not sure but it's possible that sendmail will not query
> >for the same domain the second time, thus 10,000 messages going to 5,000
> >different domains will result in only 5,000 DNS queries. Meanwhile, each
> >instance of qmail-remote should diligently issue a DNS query - for a
> >grand sum of 10,000 queries overall.
> >
> >So what you have here is 10,000 guaranteed queries from Qmail, and up to
> >10,000 DNS queries for sendmail, maybe less.
I forgot about the CNAME query when I wrote that, BTW.
> But, as the master says: "Profile, don't speculate". Take a look at:
>
> http://www.kyoto.wide.ad.jp/mta/eval1/perf1b.gif
>
> Which shows that in a test where sendmail, qmail, postfix, and other
> UNIX MTA's were given the same task, qmail was fastest. And:
>
> http://www.kyoto.wide.ad.jp/mta/eval1/perf1b+.gif
>
> Which shows that qmail started delivering messages fastest.
>
> There are numerous other charts showing qmail's measured superiority
> on:
Again, that is not always true, and Qmail will fail miserably in certain
well defined situations which do occur, quite often, in production.
--
Sam
