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

Guido(dot)Goldstein(at)t-online(dot)de (Guido Goldstein) writes:
> Eric Marsden <emarsden(at)mail(dot)dotcom(dot)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