On Tue, Jan 17, 2012, Daniel Stenberg wrote:
> On Fri, 13 Jan 2012, Pierre Ynard wrote:
> >One possibility would be to truncate the list of IP addresses to try,
>
> It would perhaps make sense if we decide that we always spend at
> least NNN milliseconds per host name so that if you put say a 5
> seconds timeout on a host name with 100 IP addresses, we still allow
> a "sensible" time for each connect attempt. Possibly that "shortest
> possible time" would be configurable and could default to something
> like 1000 or 2000 milliseconds...

I think it still makes sense without deciding on a minimum time. You
could say that libcurl never tries more than 3 (arbitrary) IP addresses.
At least you have a guarantee that a timeout no shorter than 1/3 of the
configured value will be used, and you can work with that when choosing
your timeout settings. However it's true that this approach seems not
very flexible and suboptimal. Having a configurable minimum timeout
sounds safer.

> >An interesting idea would be, instead of equally dividing 2
> >seconds, to for example try the first address for 1 second, then
> >if it fails the second one for 500 ms, then the third one for 250
> >ms and then whatever
>
> Really? If the first connect fails after a given time, is there
> really anything at all that would indicate that the next address
> would complete the connection in half the time the previous one
> didn't succeed on?

No. But spreading the range of timeout values used protects against a
wider range of failures. This way, if one IP address is down, fallback
on the next one still works, and if the host is generally slow, the
first IP has a long enough timeout to succeed; whereas dividing the
timeout equally makes libcurl resilient only against the former.

Regards,

-- 
Pierre Ynard
"Une âme dans un corps, c'est comme un dessin sur une feuille de papier."
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