From: | Florian Pflug <fgp(at)phlo(dot)org> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: augmenting MultiXacts to improve foreign keys |
Date: | 2011-08-10 08:14:10 |
Message-ID: | 8EF1FA5A-89D8-484D-BE00-2F60CF93555D@phlo.org |
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Lists: | pgsql-hackers |
On Aug9, 2011, at 22:40 , Tom Lane wrote:
> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
>> Excerpts from Jeff Davis's message of mar ago 09 14:41:14 -0400 2011:
>>> Right now, FKs aren't really very special, they are mostly just
>>> syntactic sugar (right?). This proposal would make FKs special internal
>>> mechanisms, and I don't see the benefit in doing so.
>
>> Well, you can get the same behavior by adding the constraint triggers
>> manually. But those triggers are written in C, so you could equally
>> claim that they are "special internal" already. The SPI interface has
>> some special entry points to allow them to work correctly (for example
>> passing a snapshot for the checks to run with).
>
> Yeah, the crosscheck-snapshot logic already puts the lie to any idea
> that the RI triggers are equivalent to anything available at the SQL
> level.
True, but I still considered that to be a quite unfortunate limitation,
and one that I hope to one day remove. So I'd hate to see us adding more
stumbling blocks along that road.
Even today, you can do user-space FK-like constraint if you restrict
yourself to either running all transaction in isolation level READ COMMITTED,
or all transactions in isolation level SERIALIZABLE (Though I in the later
case, you don't need locks anyway..)
best regards,
Florian Pflug
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