From: Tom Lane <tgl@sss.pgh.pa.us>
To: PG-Interfaces <pgsql-interfaces@postgreSQL.org>
Subject: Re: [INTERFACES] OIDs in pg_type stable across versions?
Date: Wed, 20 Jan 1999 10:55:28 -0500
Message-ID: <6602.916847728@sss.pgh.pa.us> (raw)
In-Reply-To: <lt7lui6oxf.fsf@Guido.Goldstein.dialup.t-online.de>
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
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To: pgsql-interfaces@postgresql.org
Cc: tgl@sss.pgh.pa.us
Subject: Re: [INTERFACES] OIDs in pg_type stable across versions?
In-Reply-To: <6602.916847728@sss.pgh.pa.us>
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