Date: Wed, 26 Sep 2018 08:52:07 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: Michael Paquier <michael@paquier.xyz>,
	Andres Freund <andres@anarazel.de>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: transction_timestamp() inside of procedures
Message-ID: <20180926125207.GA10161@momjian.us>
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 <20180921102822.GA22699@momjian.us>
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On Wed, Sep 26, 2018 at 02:38:25PM +0200, Peter Eisentraut wrote:
> On 22/09/2018 00:35, Bruce Momjian wrote:
> > I have always thought of clock/statement/transation as decreasing levels
> > of time precision, and it might be odd to change that.  I don't think we
> > want to change the behavior of statement_timestamp() in procedures, so
> > that kind of requires us not to change transaction_timestamp() inside of
> > procedures.
> > 
> > However, no change in behavior causes the problem that if you have a
> > transaction block using transaction_timestamp() or CURRENT_TIMESTAMP,
> > and you move it into a procedure, the behavior of those functions will
> > change, but this was always true of moving statement_timestamp() into a
> > function, and I have never heard a complaint about that.
> 
> Right.  Statement timestamp actually means the timestamp of the
> top-level statement, because it's set where the protocol interaction
> happens.  The transaction timestamp is implemented as the statement
> timestamp when the transaction starts, but for intra-procedural
> transactions, the statement timestamp does not advance, so the
> transaction timestamp doesn't change.
> 
> Note that this also affects the xact_start column in pg_stat_activity.
> 
> We could certainly address this by adding three or four or five new
> timestamps that cover all these varieties.  But perhaps it's worth
> asking what these timestamps are useful for and which ones we really need.

Frankly, we might be fine with just documenting it and see if anyone
complains.  I think the top-level statement part is obvious, but I am
not sure the top-level transaction part is.  This is because it is clear
the top-level statement causes all the lower statements underneath it,
but the top-level transaction doesn't control all the transactions under
it in the same way.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +