Subject: Re: Changing the transaction isolation level within the
From: Mario Splivalo <mario.splivalo@mobart.hr>
Reply-To: mario.splivalo@mobart.hr
To: Markus Schaber <schabi@logix-tt.com>
Cc: pgsql-sql@postgresql.org
In-Reply-To: <43D79132.9050900@logix-tt.com>
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	<43D79132.9050900@logix-tt.com>
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Organization: Mob-Art
Date: Thu, 26 Jan 2006 08:11:03 +0100
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On Wed, 2006-01-25 at 15:54 +0100, Markus Schaber wrote:
> Hi, Mario,
> 
> Mario Splivalo wrote:
> > Is it possible to change the transaction level within the procedure?
> 
> No, currently not, the PostgreSQL "stored procedures" really are "stored
> functions" that are called inside a query, and thus cannot contain inner
> transactions.

Is above true for the newly introduced stored procedures? (Above, when
mentioning 'stored procedures' I was actualy reffering to 'functions').

> > I'm using Postgres 8.1.2 default isolation level. But, I would like one
> > stored procedure to execute as in serializable isolation level. I have
> > created my stored procedure like this:
> [...]
> > One thread (thread A) does this:
> > 
> > 1. java got the message via http (whatever)
> > 2. java does: begin;
> > 3. java does: select * from create_message(...)
> > 4. java does some checking
> > 5. java does: select * from set_message_status(...)
> > 6. java does some more checing
> > 7. java does commit; (under rare circumstances java does rollback).
> 
> So you even want to change the transaction serialization level within a
> running transaction? I'm sorry, this will not work, and I cannot think
> of a sane way to make it work.

I have some ideas, I just needed confirmation it can't be done this way.
Thank you! :)

> It is locically not possible to raise the isolation level when the
> transaction was started with a lower level and thus may already have
> irreversibly violated the constraits that the higher level wants to
> guarantee.

Yes, a thread will need to start a transaction, I'm just affraid that
create_message could lead me to deadlocks.

Thank you for your responses.

	Mario