Message-ID: <4293171B.4040406@archonet.com>
Date: Tue, 24 May 2005 12:59:23 +0100
From: Richard Huxton <dev@archonet.com>
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To: Rafa Couto <rafacouto@gmail.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Transaction in plpgslq
References: <22df564b05052003479481da1@mail.gmail.com>
In-Reply-To: <22df564b05052003479481da1@mail.gmail.com>
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Rafa Couto wrote:
> I have got a plpgsql function:

>   -- BEGIN;
> 
>     SELECT min(id) INTO _contacto_id FROM contactos 
>       WHERE contactos.operadora_id IS NULL AND contactos.actividad_id
> = _actividad_id;
> 
>     UPDATE contactos SET operadora_id = _operadora_id WHERE id = _contacto_id;
> 
>   -- COMMIT;

> and it works right, but I need atomic execution from --BEGIN and
> --COMMIT, and manual says it is not possible to have transactions in
> PL/pgSQL procedures :-(

OK - the WHOLE FUNCTION takes place within one transaction. So, in that 
sense all changes are atomic.

However, if you want to prevent any changes to "contactos" in-between 
those two statements you'll want additional locks. Read the chapter on 
"concurrency control" for details. You might well want SELECT FOR UPDATE 
  (and also just ORDER BY id LIMIT 1 rather than using min(id)).

-- 
   Richard Huxton
   Archonet Ltd