Ok, that adds some clarity. Have base types (int32, etc) had the same
oid values for a significant number of versions of PgSQL? What I am
getting at is this: can I hard code oid values into an access layer for
PgSQL? I see that the Java driver uses select statements back into the
db to determine the datatype for a given oid. I know for user-defined
types that is required, but for base types is it required?
And thanks for the reply!
Reggie
> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> Sent: Sunday, January 05, 2003 12:42 AM
> To: Reggie Burnett
> Cc: pgsql-hackers@postgresql.org
> Subject: Re: [HACKERS] pgsql oid question
>
> "Reggie Burnett" <rykr@bellsouth.net> writes:
> > I have started experimenting with an access layer for pgsql and have
a
> > question. I had someone on this list tell me that the oid values
that
> > come back from the server are tag identifiers for that row/column
> > combination and are not type indicators.
>
> I think your someone is confused. There are no identifiers associated
> with row/column combinations.
>
> > Yet, when I create multiple
> > tables/columns each having the same type (int32), the same oid keeps
> > being returned.
>
> The OIDs returned in RowDescription messages uniquely identify
datatypes
> (more specifically, pg_type rows). They will be stable short of DROP
> TYPE/CREATE TYPE shenanigans. (However, user-defined types might not
> get the same OIDs assigned after a dump/reload cycle. It's probably
> reasonable to treat type OIDs as stable for the life of a connection,
> but not as constants of nature.)
>
> OIDs are also used for other purposes, so your confusion may stem from
> confusing pg_type OIDs with other OIDs. In the current system
> implementation, OIDs are unique row identifiers only within individual
> tables --- perhaps not even then, if the table doesn't have a unique
> index on its OID field. Thus, a pg_type OID uniquely identifies a
> datatype, but that doesn't mean that the same OID number could not
> appear in pg_class, pg_rewrite, or other system or user tables.
>
> regards, tom lane
