Re: droped out precise time calculations in src/interfaces/libpq/fe-connect.c

Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > Tom Lane wrote:
> >> That is odd; seems like you should get between 1 and 2 seconds. How
> >> were you measuring the delay, exactly?
>
> > Remember, that if you add 1, the select() is going to get tv_sec = 2, so
> > yes, it will be two seconds.
>
> Yeah, but only if the value isn't recalculated shortly later. Consider
>
> caller computes finish_time = time() + timeout;
>
> ...
>
> inside select-wait loop, compute max_delay = finish_time - time();
>
> If the time() value has incremented by 1 second between these two lines
> of code, you have a problem with a 1-second timeout...

Yep. If you track finish time, you get that 1 second rounding problem,
and if you track just duration/timeout, you get into the problem of not
knowing when the timeout has ended. I don't think these can be fixed
except by overestimating (+1) or by tracking subseconds along with
seconds so you really know when one second has elapsed.

Perhaps we need to modify a timeout of 1 to be 2 and leave other values
alone.

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