From: Tom Lane <tgl@sss.pgh.pa.us>
To: Dominique Devienne <ddevienne@gmail.com>
cc: pgsql-general@postgresql.org
Subject: Re: libpq v17 PQsocketPoll timeout is not granular enough
In-reply-to: <CAFCRh-8hf=7V8UoF63aLxSkeFmXX8-1O5tRxHL61Pngb7V9rcw@mail.gmail.com>
References: <CAFCRh-8hf=7V8UoF63aLxSkeFmXX8-1O5tRxHL61Pngb7V9rcw@mail.gmail.com>
Comments: In-reply-to Dominique Devienne <ddevienne@gmail.com>
	message dated "Mon, 10 Jun 2024 16:36:03 +0200"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <740206.1718036299.1@sss.pgh.pa.us>
Date: Mon, 10 Jun 2024 12:18:19 -0400
Message-ID: <740207.1718036299@sss.pgh.pa.us>
Archived-At: <https://www.postgresql.org/message-id/740207.1718036299%40sss.pgh.pa.us>
Precedence: bulk

Dominique Devienne <ddevienne@gmail.com> writes:
> PQsocketPoll() being based on time_t, it has only second resolution, AFAIK.
> Despite the [underlying implementation in fe-misc.c][2] supporting at
> least milliseconds.
> ...
> But I think it would a pity if that unreleased API couldn't be made to
> accomodate sub-second timeouts and more use-cases, like above.
> Especially given that libpq v17 isn't out yet. I may come late to the
> game, but hopefully it is not too late.

This is an interesting suggestion, but I think yes it's too late.
We're already past beta1 and this'd require some fairly fundamental
rethinking, since there's no easy substitute for type time_t that has
millisecond resolution.  (The callers do want to specify an end time
not a timeout interval, since some of them loop around PQsocketPoll
and don't want the end time to slip.)

I guess conceivably we could use gettimeofday() and struct timeval
instead of time() and time_t, but it'd touch a lot of places in
libpq and it'd make some of the calculations a lot more complex.

Maybe a better idea would be to convert to using our
src/include/portability/instr_time.h abstraction?  But that
would be problematic for outside callers.

In any case this doesn't seem like a sane thing to be redesigning
post-beta.  A few months ago maybe we'd have done it, but ...

			regards, tom lane