Received: from malur.postgresql.org ([2a02:16a8:dc51::56])
	by arkaria.postgresql.org with esmtps
 (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256)
	(Exim 4.89)
	(envelope-from <pgsql-hackers-owner+archive@lists.postgresql.org>)
	id 1g8Qb2-0002qM-1V
	for pgsql-hackers@arkaria.postgresql.org; Fri, 05 Oct 2018 13:56:48 +0000
Received: from localhost ([127.0.0.1] helo=malur.postgresql.org)
	by malur.postgresql.org with esmtp (Exim 4.89)
	(envelope-from <pgsql-hackers-owner+archive@lists.postgresql.org>)
	id 1g8Qaz-0000ex-JA
	for pgsql-hackers@arkaria.postgresql.org; Fri, 05 Oct 2018 13:56:45 +0000
Received: from makus.postgresql.org ([2001:4800:1501:1::229])
	by malur.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256)
	(Exim 4.89)
	(envelope-from <tgl@sss.pgh.pa.us>)
	id 1g8Qaz-0000eq-95
	for pgsql-hackers@lists.postgresql.org; Fri, 05 Oct 2018 13:56:45 +0000
Received: from sss.pgh.pa.us ([66.207.139.130])
	by makus.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256)
	(Exim 4.89)
	(envelope-from <tgl@sss.pgh.pa.us>)
	id 1g8Qaw-0006Ko-MX
	for pgsql-hackers@postgresql.org; Fri, 05 Oct 2018 13:56:44 +0000
Received: from sss1.sss.pgh.pa.us (localhost [127.0.0.1])
	by sss.pgh.pa.us (8.14.4/8.14.4) with ESMTP id w95DuZ6X004269;
	Fri, 5 Oct 2018 09:56:35 -0400
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: now() vs transaction_timestamp()
In-reply-to: <6406dbd2-5d37-4cb6-6eb2-9c44172c7e7c@postgrespro.ru>
References: <6406dbd2-5d37-4cb6-6eb2-9c44172c7e7c@postgrespro.ru>
Comments: In-reply-to Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
	message dated "Fri, 05 Oct 2018 16:29:28 +0300"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <4267.1538747795.1@sss.pgh.pa.us>
Date: Fri, 05 Oct 2018 09:56:35 -0400
Message-ID: <4268.1538747795@sss.pgh.pa.us>
List-Id: <pgsql-hackers.lists.postgresql.org>
List-Help: <https://lists.postgresql.org/manage/>
List-Subscribe: <https://lists.postgresql.org/manage/>
List-Post: <mailto:pgsql-hackers@lists.postgresql.org>
List-Owner: <mailto:pgsql-hackers-owner@lists.postgresql.org>
List-Archive: <https://www.postgresql.org/list/pgsql-hackers>
Precedence: bulk

Konstantin Knizhnik <k.knizhnik@postgrespro.ru> writes:
> Postgres documentation says that |"now()| is a traditional PostgreSQL 
> equivalent to |transaction_timestamp()|".
> Also both use the same implementation.

Right.

> But them have different parallel safety property:

That seems like a bug/thinko.  I am not sure which property setting is
correct though.  It'd only be safe if the parallel-query infrastructure
transfers the relevant timestamp to workers, and I don't know if it does.

			regards, tom lane