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Re: Transaction Questions

From: Richard Kut <rkut(at)intelerad(dot)com>
To: Sean Davis <sdavis2(at)mail(dot)nih(dot)gov>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-novice(at)postgresql(dot)org, Mathew Kanner <Mathew(dot)Kanner(at)intelerad(dot)com>
Subject: Re: Transaction Questions
Date: 2006-02-24 20:14:11
Message-ID: 200602241514.11144.rkut@intelerad.com (view raw or flat)
Thread:
Lists: pgsql-novice
Hi Sean!

	I tried it, but it did not help. Here is the output:

xyz=> TRUNCATE TABLE t1;
TRUNCATE TABLE
xyz=> BEGIN;
BEGIN
xyz=>   SAVEPOINT p1;
SAVEPOINT
xyz=>   INSERT INTO t1 VALUES ('w', 1);
INSERT 0 1
xyz=>   RELEASE SAVEPOINT p1;
RELEASE
xyz=>   SELECT * FROM t1;
 c1 | n1
----+----
 w  |  1
(1 row)

xyz=>   SAVEPOINT p2;
SAVEPOINT
xyz=>   INSERT INTO t1 VALUES ('w', 1);
ERROR:  duplicate key violates unique constraint "t1_c1_idx"
xyz=>   RELEASE SAVEPOINT p2;
ERROR:  current transaction is aborted, commands ignored until end of 
transaction block
xyz=> END;
ROLLBACK
xyz=> SELECT * FROM t1;
 c1 | n1
----+----
(0 rows)

xyz=>                                                


On Friday 24 February 2006 15:08, Sean Davis wrote:
> On 2/24/06 2:47 PM, "Richard Kut" <rkut(at)intelerad(dot)com> wrote:
> > Hi Tom!
> >
> >>> BEGIN
> >>>   INSERT
> >>>     OR UPDATE
> >>>   INSERT
> >>>      OR UPDATE
> >>> COMMIT
> >>>
> >>> Suppose the second INSERT fails with a duplicate key,  we cannot do the
> >>> update (or get the previous INSERT) because the ROLLBACK is mandatory.
> >>
> >> No it isn't.  You say SAVEPOINT, then do the INSERT, then say either
> >> RELEASE SAVEPOINT if the insert succeeded, or ROLLBACK TO SAVEPOINT
> >> if the insert failed.  (RELEASE is actually optional here, but might
> >> make things a bit more transparent.)  Then you go on with your
> >> transaction.
> >
> > I tried what you suggested, and here are the results:
> >
> > xyz=> TRUNCATE TABLE t1;
> > TRUNCATE TABLE
> > xyz=> BEGIN;
> > BEGIN
> > xyz=>   SAVEPOINT p1;
> > SAVEPOINT
> > xyz=>   INSERT INTO t1 VALUES ('w', 1);
> > INSERT 0 1
> > xyz=>   RELEASE SAVEPOINT p1;
> > RELEASE
> > xyz=>   SELECT * FROM t1;
> >  c1 | n1
> > ----+----
> >  w  |  1
> > (1 row)
> >
> > xyz=>   SAVEPOINT p2;
> > SAVEPOINT
> > xyz=>   INSERT INTO t1 VALUES ('w', 1);
> > ERROR:  duplicate key violates unique constraint "t1_c1_idx"
>
> You need another RELEASE SAVEPOINT here, I think.
>
> > xyz=> END;
> > ROLLBACK
> > xyz=> SELECT * FROM t1;
> >  c1 | n1
> > ----+----
> > (0 rows)
> >
> > xyz=>
> >
> >> The problem is that you are using transaction-ending
> >> commands where you should be using savepoint-ending commands.
> >
> > As far as I know, transaction-ending commands are ROLLBACK, ABORT, and
> > COMMIT. I do not know of any others, and I have no idea what you mean
> > about savepoint-ending. Please explain.

-- 
Regards,

Richard Kut
Database Administrator
Research & Development
Intelerad Medical Systems Inc.
460 Ste-Catherine West, Suite 210
Montreal, Quebec, Canada H3B 1A7
Tel:     514.931.6222 x7733
Fax:     514.931.4653
rkut(at)intelerad(dot)com
www.intelerad.com

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