From: Tom Lane <tgl@sss.pgh.pa.us>
To: Rob Sargent <robjsargent@gmail.com>
cc: p.sun.fun@gmail.com,
        "pgsql-sql@lists.postgresql.org" <pgsql-sql@lists.postgresql.org>
Subject: Re: libpq CREATE DATABASE operation from multiple treads
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Comments: In-reply-to Rob Sargent <robjsargent@gmail.com>
	message dated "Thu, 08 Oct 2020 14:50:31 -0600"
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Date: Thu, 08 Oct 2020 16:56:28 -0400
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Rob Sargent <robjsargent@gmail.com> writes:
> OK, well that’s a special db.  Didn’t know it was that special, though!

It's not that special.  The issue here is that each session is connecting
to template1 and then trying to clone template1.  You can't clone an
active database, because you might not get a consistent copy.  CREATE
DATABASE knows that its own session isn't concurrently making any
changes, so it allows copying the current database --- but it can't
know what some other session is doing, so if it sees some other session
is also connected to the source database, it spits up.

As I already said, routinely connecting to template1 is pretty bad
practice to start with, so the preferred answer is "don't do that".

			regards, tom lane