Re: CURRENT OF cursor without OIDs

Hiroshi Inoue <Inoue@tpf.co.jp> writes:

> > > > Ian Lance Taylor <ian@airs.com> writes:
> > > > > Anyhow, I see that there is a move afoot to eliminate mandatory OIDs.
> > > > > My question now is: if there is no OID, is there any comparable way to
> > > > > implement CURRENT OF cursor?  Basically what is needed is some way to
> > > > > identify a particular row between a SELECT and an UPDATE.
> > > >
> > > > I'd look at using TID.  Seems like that is more efficient anyway (no
> > > > index needed).  Hiroshi has opined that TID is not sufficient for ODBC
> > > > cursors, but it seems to me that it is sufficient for SQL cursors.
> > > >
> > >
> > > Yes TID is available and I introduced Tid Scan in order
> > > to support this kind of implementation. However there
> > > are some notices.
> > > 1) Is *FOR UPDATE* cursor allowed in PL/pgSQL ?
> > >    (It doesn't seem easy for me).
> > 
> > No, it is not supported right now.
> > 
> > Conceptually, however, PL/pgSQL could pull out the FOR UPDATE clause
> > and turn it into an explicit LOCK statement.
> 
> It's impossible to realize *FOR UPDATE* using LOCK statement.
> Each row must be locked individually to prevent UPDATE/DELETE
> operations for the row. You could acquire an EXCLUSIVE
> LOCK on the table but it doesn't seem preferable.

It's definitely not preferable, but how else can it be done?

> I'm planning to implement updatable cursors with no lock
> using TID and OID. TID is for the fast access and OID is
> to verify the identity. OID doesn't provide a specific
> access method in the first place and the access would be
> veeery slow for large tables unless there's an index on OID.

I apologize if I've missed something, but how will that work when OIDs
become optional?

Ian