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Message-ID: <4A680C03.6040701@gmail.com>
Date: Thu, 23 Jul 2009 17:06:43 +1000
From: Chris <dmagick@gmail.com>
User-Agent: Thunderbird 2.0.0.22 (X11/20090608)
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To: Joshua Tolley <eggyknap@gmail.com>
CC: Glenn Maynard <glenn@zewt.org>, Richard Huxton <dev@archonet.com>,
	pgsql-sql@postgresql.org
Subject: Re: Bit by "commands ignored until end of transaction block"
 again
References: <bd36f99e0907222158k6b4b3a0al65766c0d9c4906cf@mail.gmail.com>
	<4A67F5B6.4080409@archonet.com>
	<bd36f99e0907222304x38cfa50bkeba19f7c9b2694@mail.gmail.com>
	<20090723064656.GO25450@eddie>
In-Reply-To: <20090723064656.GO25450@eddie>
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Joshua Tolley wrote:
> On Thu, Jul 23, 2009 at 02:04:53AM -0400, Glenn Maynard wrote:
>> On Thu, Jul 23, 2009 at 1:31 AM, Richard Huxton<dev@archonet.com> wrote:
>>>>  - Let me use SAVEPOINT outside of a transaction,
>>> You are never outside a transaction. All queries are executed within a
>>> transaction.
>> "Transaction block", then, if you insist.
>>
>>> I think this is the root of your problem - all queries are within a
>>> transaction so either:
>>> 1. You have a transaction that wraps a single statement. If you get an error
>>> then only that statement was affected.
>>> 2. You have an explicit BEGIN...COMMIT transaction which could use a
>>> savepoint.
>> Savepoints can only be used inside transaction blocks.  My function
>> has no idea whether it's being called inside a transaction block.
>>
>> From inside a transaction block, my function would need to call
>> SAVEPOINT/RELEASE SAVEPOINT.
>>
>> If it's not in a transaction block, it needs to call BEGIN/COMMIT
>> instead.  SAVEPOINT will fail with "SAVEPOINT can only be used in
>> transaction blocks".
> 
> Have you tried this? I expect if you give it a shot, you'll find you don't
> actually have this problem. Really, everything is always in a transaction.

Each statement is in it's own transaction, but the problem (as I 
understand it) is that you're in this sort of situation:

psql -d dbname
..
# select now();
               now
-------------------------------
  2009-07-23 17:04:21.406424+10
(1 row)

Time: 2.434 ms
(csmith@[local]:5432) 17:04:21 [test]
# savepoint xyz;
ERROR:  SAVEPOINT can only be used in transaction blocks
(csmith@[local]:5432) 17:04:25 [test]


You haven't explicitly started a transaction, therefore savepoints won't 
work.

Django (it seems) just issues queries with no knowledge of (and no way 
to support) them.

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