Re: transction_timestamp() inside of procedures

On Fri, Sep 21, 2018 at 06:28:22AM -0400, Bruce Momjian wrote:
> On Fri, Sep 21, 2018 at 02:34:25PM +0900, Michael Paquier wrote:
> > On Thu, Sep 20, 2018 at 10:12:06PM -0700, Andres Freund wrote:
> > > Isn't the point that transaction_timestamp() does *not* currently change
> > > its value, even though the transaction (although not the outermost
> > > statement) has finished?
> > 
> > Ouch, yes.  I see the point now.  Indeed that's strange to not have a
> > new transaction timestamp after commit within the DO block..
> 
> So, this puts us in an odd position.  Right now everyone knows that
> statement_timestamp() is only changed by the outer statement, i.e., a
> SELECT in a function doesn't change statement_timestamp().   So, there
> is an argument that transaction_timestamp() should do the same and not
> change in a function --- in fact, if it does change, it would mean that
> transaction_timestamp() changes in a function, but statement_timestamp()
> doesn't --- that seems very odd.  It would mean that new statements in a
> function don't change statement_timestamp(), but new transctions in a
> function do --- again, very odd.

Sorry I was unclear about this.  It is only the third loop that proves
it is not advancing:

    NOTICE:  clock       2018-09-21 18:01:00.63704-04
    NOTICE:  statement   2018-09-21 18:01:00.636509-04
    NOTICE:  transaction 2018-09-21 18:01:00.636509-04
    
    NOTICE:  clock       2018-09-21 18:01:02.640033-04
    NOTICE:  statement   2018-09-21 18:01:00.636509-04
    NOTICE:  transaction 2018-09-21 18:01:00.636509-04
    
    NOTICE:  clock       2018-09-21 18:01:04.642266-04
    NOTICE:  statement   2018-09-21 18:01:00.636509-04
-->    NOTICE:  transaction 2018-09-21 18:01:00.636509-04

Keep in mind that transaction_timestamp() is CURRENT_TIMESTAMP.  

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.

Does the SQL standard have anything to say about CURRENT_TIMESTAMP in
procedures?  Do we need another function that does advance on procedure
commit?

-- 
  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 +