Zitat von Victor Duchovni <victor.ducho...@morganstanley.com>:
On Mon, Nov 15, 2010 at 09:47:07AM -0500, Wietse Venema wrote:> > With smtp_host_lookup=dns, all SMTP client lookups are sequential. > > With smtp_host_lookup=native (or dns,native) Postfix in dual-protocol > > mode will invoke getaddrinfo() with hints.ai_family=PF_UNSPEC. > > The internals of getaddrinfo() are system dependent. > > From what i can see i don't want "smtp_host_lookup=native" for > potential side-effects, but do i get it right that it is still unsure > if the lookup is done in parallel or not when using "native"? That is operating system dependent.In other words, "native" lookup behaviour is out of Postfix's hands. As for "dns" lookups, Postfix looks up "AAAA" and "A" records sequentially, async DNS libraries are not standard with most systems, so it is not possible to issue two DNS queries and wait for both to complete, without using threads, which is a non-starter, or calling out to external helper processes (which is not terribly attractive). At this time, it probably does not make sense for Postfix to bundle an async DNS lookup library with its source code. Conditionally compiling-in support for such a library is a bit painful, though opendkim seems to have taken that approach. They have a DNS lookup driver layer, and the driver reports whether it can support overlapping queries... You can then choose to use an async DNS library if you have one.
Thanks for explaining the details. I don't really have the traffic to care about this "limitation", it was more of to learn about implications on deploying IPv6 in a network with different services running and to get knowledge where problems might arise.
Regards Andreas
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