Re: almost-super-user problems that we haven't fixed yet

From: Nathan Bossart <nathandbossart(at)gmail(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: almost-super-user problems that we haven't fixed yet
Date: 2023-01-18 21:14:14
Message-ID: 20230118211414.GA3702050@nathanxps13
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On Wed, Jan 18, 2023 at 02:51:38PM -0500, Robert Haas wrote:
> Should (nfree < SuperuserReservedBackends) be using <=, or am I confused?

I believe < is correct. At this point, the new backend will have already
claimed a proc struct, so if the number of remaining free slots equals the
number of reserved slots, it is okay.

> What's the deal with removing "and no new replication connections will
> be accepted" from the documentation? Is the existing documentation
> just wrong? If so, should we fix that first? And maybe delete
> "non-replication" from the error message that says "remaining
> connection slots are reserved for non-replication superuser
> connections"? It seems like right now the comments say that
> replication connections are a completely separate pool of connections,
> but the documentation and the error message make it sound otherwise.
> If that's true, then one of them is wrong, and I think it's the
> docs/error message. Or am I just misreading it?

I think you are right. This seems to have been missed in ea92368. I moved
this part to a new patch that should probably be back-patched to v12.

On that note, I wonder if it's worth changing the "sorry, too many clients
already" message to make it clear that max_connections has been reached.
IME some users are confused by this error, and I think it would be less
confusing if it pointed to the parameter that governs the number of
connection slots. I'll create a new thread for this.

Nathan Bossart
Amazon Web Services:

Attachment Content-Type Size
v3-0001-Code-review-for-ea92368.patch text/x-diff 1.6 KB
v3-0002-Rename-ReservedBackends-to-SuperuserReservedBacke.patch text/x-diff 4.0 KB
v3-0003-Introduce-reserved_connections-and-pg_use_reserve.patch text/x-diff 12.8 KB

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