Re: Nested transactions and tuple header info

On Wed, Jun 02, 2004 at 09:52:28AM -0400, Tom Lane wrote:

> BEGIN;
> DECLARE CURSOR c1 FOR SELECT * FROM a ...;
> INSERT INTO a VALUES(...); -- call this row x
> DECLARE CURSOR c2 FOR SELECT * FROM a ...;
> BEGIN;
> DELETE FROM a WHERE ...; -- assume this deletes row x
> ROLLBACK;
> FETCH FROM c1; -- must NOT see row x
> FETCH FROM c2; -- must see row x
>
> AFAICS your proposal does not support this. The two cursors' snapshots
> will differ only in the recorded current-cid for the outer transaction.
> If the subtrans has overwritten xmin/cmin, there is no way to make that
> decision correctly.

Why would it overwrite cmin? Only a new xmin is needed (and cmax and
xmax, but the cursors don't care about those)

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"La fuerza no está en los medios físicos
sino que reside en una voluntad indomable" (Gandhi)