From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
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To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com>, Pavan Deolasee <pavan(dot)deolasee(at)2ndquadrant(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [HACKERS] MERGE SQL Statement for PG11 |
Date: | 2018-03-08 22:46:13 |
Message-ID: | CAH2-WzmnQ81DGDdjD=F1zV_2aS+9oTnM489nzsFJSQu+9nOTCg@mail.gmail.com |
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On Thu, Mar 8, 2018 at 6:52 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> I removed this code since it was wrong. We might want to add some basic
>> checks for existence of volatile functions in the WHEN or SET clauses. But I
>> agree, it's no different than regular UPDATEs. So may be not a big deal.
>
> I just caught up on this thread. I'm definitely glad to see that code
> go because, wow, that is all kinds of wrong. I don't see a real need
> to add any kind of replacement check, either. Prohibiting volatile
> functions here doesn't seem likely to accomplish anything useful. It
> seems like the most we'd want to do is mention this the documentation
> somehow, and I'm not even sure we really need to do that much.
Thanks in large part to Pavan's excellent work, the situation in
nodeModifyTable.c is much clearer than it was a few weeks ago. It's
now obvious that MERGE is very similar to UPDATE ... FROM, which
doesn't have any restrictions on volatile functions.
I don't see any sense in prohibiting volatile functions in either
case, because it should be obvious to users that that's just asking
for trouble. I can believe that someone would make that mistake, just
about, but they'd have to be writing their DML statement on
auto-pilot.
--
Peter Geoghegan
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