From: Tom Lane <tgl@sss.pgh.pa.us>
To: Holger Jakobs <holger@jakobs.com>
cc: pgsql-admin <pgsql-admin@postgresql.org>
Subject: Re: now() and statement_timestamp()
In-reply-to: <536812b3-8040-371d-506d-266bcf10ec2f@jakobs.com>
References: <536812b3-8040-371d-506d-266bcf10ec2f@jakobs.com>
Comments: In-reply-to Holger Jakobs <holger@jakobs.com>
	message dated "Thu, 27 May 2021 18:26:42 +0200"
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Date: Thu, 27 May 2021 12:43:56 -0400
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Holger Jakobs <holger@jakobs.com> writes:
> So in psql now() and statement_timestamp() are identical when not in a 
> transaction, while in the others the two values vary a little bit, 
> roughly 100 microseconds.

> How come the same statements aren't behaving identical. I'm using a 
> current PostgreSQL server on a Linux machine.

I'd try turning on log_statement = all to see what's actually
happening.  What seems somewhat likely is that the non-psql
cases are wrapping the command you gave in BEGIN/COMMIT,
or something along that line.

[ thinks for a bit ]  It could also be down to the wire protocol
used.  psql is just sending a simple Query message, but the
other two might well be sending Parse/Bind/Execute.  IIRC the
transaction must be started by Bind, but we may consider
the statement timestamp to be the start of processing Execute.

			regards, tom lane