From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Stephen Frost <sfrost(at)snowman(dot)net>, Peter Geoghegan <pg(at)bowt(dot)ie>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: MERGE SQL Statement for PG11 |
Date: | 2017-11-03 14:16:03 |
Message-ID: | CANP8+j+JxXs8RWWpz2yRZdbWMti6M5rxyKZDY-yLvDt3ROOYMA@mail.gmail.com |
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Lists: | pgsql-hackers |
On 3 November 2017 at 08:26, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Fri, Nov 3, 2017 at 1:05 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>>> Therefore, if MERGE eventually uses INSERT .. ON CONFLICT
>>> UPDATE when a relevant unique index exists and does something else,
>>> such as your proposal of taking a strong lock, or Peter's proposal of
>>> doing this in a concurrency-oblivious manner, in other cases, then
>>> those two cases will behave very differently.
>>
>> The *only* behavioural difference I have proposed would be the *lack*
>> of an ERROR in (some) concurrent cases.
>
> I think that's a big difference. Error vs. non-error is a big deal by
> itself;
Are you saying avoiding an ERROR is a bad or good thing?
> also, the non-error case involves departing from MVCC
> semantics just as INSERT .. ON CONFLICT UPDATE does.
Meaning what exactly? What situation occurs that a user would be concerned with?
Please describe exactly what you mean so we get it clear.
The concurrent behaviour for MERGE is allowed to be
implementation-specific, so we can define it any way we want.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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