
> Who wants subtransactions with UNDO and who wants it with a separate
> transaction id for every subtransaction?

I think there is at least one special case, that would largely profit 
from UNDO (or some other identical mechanism), namely an insert that 
causes a constraint violation.

The standard way to program an "insert or update" is to do the one command 
that will succeed in more cases first, then on failure do the other.
In PG this currently has to be done inefficiently by first doing the update
and then doing the insert. If we had implicit subtransactions, I think people 
would start using the standard approach. It would probably not be too nice if 
that would always leave dead tuples and index entries around.

Andreas


Tue, 1 Apr 2003 19:32:24 +0200
"Zeugswetter Andreas SB SD" <ZeugswetterA@spardat.at>
Re: Nested transactions: low level stuff