Date: Fri, 11 Jan 2013 17:31:13 +0100
From: Andres Freund <andres@2ndquadrant.com>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Erik Rijkers <er@xs4all.nl>, Kevin Grittner <kgrittn@mail.com>,
	pgsql-hackers@postgresql.org
Subject: Re: foreign key locks
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On 2013-01-11 13:10:49 -0300, Alvaro Herrera wrote:
> Andres Freund wrote:
>
> > No, I was thinking about an update without triggers present.
> >
> > T0: CREATE TABLE tbl(id serial pk, name text unique, data text);
> > T1: BEGIN; -- read committed
> > T1: UPDATE tbl SET name = 'foo' WHERE name = 'blarg'; /* key update of row id = 1 */
> > T2: BEGIN; -- read committed
> > T2: UPDATE tbl SET name = 'blarg', data = 'blarg' WHERE id = 1; /* no key update, waiting */
> > T1: COMMIT;
> > T2: /* UPDATE follows to updated row, due to the changed name its a key update now */
> >
> > Does that make sense?
>
> So I guess your question is "is T2 now holding a TupleLockExclusive
> lock?"  To answer it, I turned your example into a isolationtester spec:

Great! I reread the code and it does make sense the way its implemented
now. I misremembered something...

I vote for adding that spectest including some appropriate permutations.

FWIW: Looks good to me. It could use another pair of eyes, but I guess
that will have to come by being used.

Greetings,

Andres Freund

--
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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