From: Tom Lane <tgl@sss.pgh.pa.us>
To: Greg Sabino Mullane <htamfids@gmail.com>
cc: Antonin Houska <ah@cybertec.at>,
        "pgsql-hackers@lists.postgresql.org"
 <pgsql-hackers@lists.postgresql.org>
Subject: Re: POC: Carefully exposing information without authentication
In-reply-to: 
 <CAKAnmmJ77jeYZGXPBxb75U52ojNRUoKd6Za-T26xNPCouUeV8g@mail.gmail.com>
References: 
 <CAKAnmm+T-CEDLmRezWfH-7ZEsFfD_kU2KY1TgB288K+wprB_4Q@mail.gmail.com>
 <21076.1748617331@localhost>
 <CAKAnmmJ77jeYZGXPBxb75U52ojNRUoKd6Za-T26xNPCouUeV8g@mail.gmail.com>
Comments: In-reply-to Greg Sabino Mullane <htamfids@gmail.com>
	message dated "Fri, 30 May 2025 20:13:45 -0400"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <2724611.1748655287.1@sss.pgh.pa.us>
Date: Fri, 30 May 2025 21:34:47 -0400
Message-ID: <2724612.1748655287@sss.pgh.pa.us>
Archived-At: 
 <https://www.postgresql.org/message-id/2724612.1748655287%40sss.pgh.pa.us>
Precedence: bulk

Greg Sabino Mullane <htamfids@gmail.com> writes:
> Good question. Forking is expensive, and there is also a lot of
> housekeeping associated with it that is simply not needed here. We want
> this to be lightweight, and simple. No need to fork if we are just going to
> do a few strncmp() calls and a send().

send() can block.  I think calling it in the postmaster is a
nonstarter.  For comparison, we make an effort to not do any
communication with incoming clients until after forking a child
to do the communication.  The one exception is if we have to
report fork failure --- but we don't make any strong guarantees
about that report succeeding.  (IIRC, we put the port into nonblock
mode and try only once.)  That's probably not a behavior you want
to adopt for non-edge-case usages.

Another point is that you'll recall that there's a lot of
interest in switching to a threaded model.  The argument that
"fork is too expensive" may not have a long shelf life.

I'm not taking a position on whether $SUBJECT is a good idea
in the first place.

			regards, tom lane