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OIDs in pg_type stable across versions? 3+ messages / 3 participants [nested] [flat]
* OIDs in pg_type stable across versions? @ 1999-01-20 10:16 Eric Marsden <emarsden@mail.dotcom.fr> 0 siblings, 1 reply; 3+ messages in thread From: Eric Marsden @ 1999-01-20 10:16 UTC (permalink / raw) To: pgsql-interfaces Hello, I have written a socket-level interface to PostgreSQL for scsh, an implementation of the Scheme programming language which provides a POSIX interface. Unlike Tcl or Perl, Scheme distinguishes between numbers and strings and booleans and so on (it's a real programming language :), so I'm looking at how it might be possible to convert data retrieved from the backend as a character stream into the appropriate Scheme types. The fe-be protocol seems to provide sufficient information to do this type coercion: when the backend sends the attribute data in response to a SELECT statement, it sends a sequence of tuples (name, type-id, size). The type-id is an OID from the pg_type table. 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? (or maybe there's some simpler way to do the type coercions?) -- Eric Marsden emarsden @ mail.dotcom.fr It's elephants all the way down ^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: [INTERFACES] OIDs in pg_type stable across versions? @ 1999-01-20 13:42 Guido Goldstein <Guido.Goldstein@t-online.de> parent: Eric Marsden <emarsden@mail.dotcom.fr> 0 siblings, 1 reply; 3+ messages in thread From: Guido.Goldstein@t-online.de @ 1999-01-20 13:42 UTC (permalink / raw) To: pgsql-interfaces Moin! On 20 Jan 1999 11:16:31 +0100 Eric Marsden <emarsden@mail.dotcom.fr> wrote: [snipped - low level interface for scheme] > The fe-be protocol seems to provide sufficient information to do this > type coercion: when the backend sends the attribute data in response > to a SELECT statement, it sends a sequence of tuples (name, type-id, > size). The type-id is an OID from the pg_type table. > > 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. 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. > (or maybe there's some simpler way to do the type coercions?) Not in my field of vision. HAND Guido -- In the beginning there was nothing, and then even that exploded ^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: [INTERFACES] OIDs in pg_type stable across versions? @ 1999-01-20 15:55 Tom Lane <tgl@sss.pgh.pa.us> parent: Guido Goldstein <Guido.Goldstein@t-online.de> 0 siblings, 0 replies; 3+ messages in thread From: Tom Lane @ 1999-01-20 15:55 UTC (permalink / raw) To: pgsql-interfaces 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 ^ permalink raw reply [nested|flat] 3+ messages in thread
end of thread, other threads:[~1999-01-20 15:55 UTC | newest] Thread overview: 3+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 1999-01-20 10:16 OIDs in pg_type stable across versions? Eric Marsden <emarsden@mail.dotcom.fr> 1999-01-20 13:42 ` Guido Goldstein <Guido.Goldstein@t-online.de> 1999-01-20 15:55 ` Tom Lane <tgl@sss.pgh.pa.us>
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