Date: Wed, 19 Sep 2018 15:53:25 +0300
From: Arthur Zakirov <a.zakirov@postgrespro.ru>
To: Pavel Stehule <pavel.stehule@gmail.com>
Cc: Dean Rasheed <dean.a.rasheed@gmail.com>,
	Fabien COELHO <coelho@cri.ensmp.fr>,
	Gilles Darold <gilles.darold@dalibo.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: [HACKERS] proposal: schema variables
Message-ID: <20180919125324.GA31127@zakirov.localdomain>
References: 
 <CAFj8pRCyvx37Fnw6yHdscGbbGo_Ak3WdeKiZ6arFW8JTA099YA@mail.gmail.com>
 <alpine.DEB.2.21.1808230927090.31897@lancre>
 <CAFj8pRAcFv09qOcbr09c2AbwZ9DGw5Hs6rPcYoo7r9OLdWWB2A@mail.gmail.com>
 <CAEZATCVy77hhgTZ1Yrvbp6GbsUuWY0Bw8CLbv_Jr2mAF_bOkBA@mail.gmail.com>
 <CAFj8pRDREykg0hnMBkryBmSTtqEs9QUKUp_447_F5P1j8bkH1w@mail.gmail.com>
 <CAFj8pRBkPswn0JA8U3vFOdBGqcBu0ZM7jC7JcDdCS1EbZfzb2A@mail.gmail.com>
 <CAFj8pRAi2Xd93ae-SsnMOC5W4hWenmkftTnCrHgdcPpvbOs1bg@mail.gmail.com>
 <CAFj8pRCZuq=0MRsYrNzBqxPx5fqmKFN3i-BsPo8j=yW6N_=WDA@mail.gmail.com>
 <20180919112305.GA18604@zakirov.localdomain>
 <CAFj8pRA-yGAedtHeS4fDzWsJR1WqVu3TXABpF+XYrQE5fd0Dog@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: 
 <CAFj8pRA-yGAedtHeS4fDzWsJR1WqVu3TXABpF+XYrQE5fd0Dog@mail.gmail.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Precedence: bulk

On Wed, Sep 19, 2018 at 02:08:04PM +0200, Pavel Stehule wrote:
> Unfortunately we cannot to use standard
> "SET" command, because it is used in Postgres for different purpose.
> READ|WRITE are totally clear, and for user it is another signal so
> variables are different than tables (so it is not one row table).
> 
> I prefer current state, but if common opinion will be different, I have not
> problem to change it.

I see. I grepped the thread before writhing this but somehow missed the
discussion.

> The content of variables is not transactional (by default). It is not
> destroyed by rollback. So I have to calculate with rollback too. So the
> most correct syntax should be "ON COMMIT ON ROLLBACK RESET" what is little
> bit messy and I used "ON TRANSACTION END". It should be signal, so this
> event is effective on rollback event and it is valid for not transaction
> variable. This logic is not valid to transactional variables, where ON
> COMMIT RESET has sense. But this behave is not default and then I prefer
> more generic syntax.
> ...
> So I see two different cases - work with catalog (what is transactional)
> and work with variable value, what is (like other variables in programming
> languages) not transactional. "ON TRANSACTION END RESET" means - does reset
> on any transaction end.
> 
> I hope so I explained it cleanly - if not, please, ask.

I understood what you mean, thank you. I thought that
{ ON COMMIT DROP | ON TRANSACTION END RESET } parameters are used only
for transactional variables in the first place. But is there any sense
in using this parameters with non-transactional variables? That is when
we create non-transactional variable we don't want that the variable
will rollback or reset its value after the end of a transaction.

-- 
Arthur Zakirov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company