Re: [INTERFACES] OIDs in pg_type stable across versions?

Guido.Goldstein@t-online.de (Guido Goldstein) writes:
>     Eric Marsden <emarsden@mail.dotcom.fr> wrote:
>> Is is reasonable to assume that these oids will be stable across
>> versions and platforms, or will I have to reconstruct a table from
>> a `SELECT typname, oid FROM pg_type' each time a connection is
>> initiated?

> I think, yes you should. Think of user defined types! They will be
> stored in pg_types also.

Guido's right.  The predefined types (like INT4) have permanently
assigned OIDs, but array types and user-defined types are entered
into the table on-the-fly.  Just reloading the database would likely
change their OIDs, let alone moving to a different version.  Also,
I believe different databases within a single installation have
separate pg_type tables, which are likely to have only the system
types in common.

> What you can do is: cache and share this type information between all
> connections initiated from this process.  And then, from time to time,
> reload the type information -- or intercept all changes on pg_type
> ('listen' command) and reload your type infos then.

I don't think a listen on pg_type would do anything; the system doesn't
issue notifies when changing system tables, AFAIK.  But what you could
do is pull the pg_type table at connection startup, and subsequently
whenever you see a type OID that you haven't got any info about, do
"SELECT ... FROM pg_type WHERE oid = xxx" to add the info to your
table.  Under normal use that wouldn't happen very often, I imagine.

            regards, tom lane