Re: Basic DOMAIN Support - Mailing list pgsql-patches

Patch applied.  Thanks.

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Rod Taylor wrote:
> Ok.  Updated patch attached.
>
> - domain.patch -> source patch against pgsql in cvs
> - drop_domain.sgml and create_domain.sgml -> New doc/src/sgml/ref docs
> - dominfo.txt -> basic domain related queries I used for testing
>
> Enables domains of array elements -> CREATE DOMAIN dom int4[3][2];
>
> Uses a typbasetype column to describe the origin of the domain.
>
> Copies data to attnotnull rather than processing in execMain().
>
> Some documentation differences from earlier.
>
> If this is approved, I'll start working on pg_dump, and a \dD <domain>
> option in psql, and regression tests.  I don't really feel like doing
> those until the system table structure settles for pg_type.
>
>
> CHECKS when added, will also be copied to to the table attributes.  FK
> Constraints (if I ever figure out how) will be done similarly.  Both
> will lbe handled by MergeDomainAttributes() which is called shortly
> before MergeAttributes().
>
>
> Any other recommendations?
>
> --
> Rod Taylor
>
> This message represents the official view of the voices in my head
>
> ----- Original Message -----
> From: "Tom Lane" <tgl@sss.pgh.pa.us>
> To: "Rod Taylor" <rbt@zort.ca>
> Cc: <pgsql-patches@postgresql.org>
> Sent: Sunday, February 24, 2002 8:11 PM
> Subject: Re: [PATCHES] Basic DOMAIN Support
>
>
> > "Rod Taylor" <rbt@zort.ca> writes:
> > > I intend to add other parts of domain support later on (no reason
> to
> > > hold up committing this though) but would appreciate some feedback
> > > about what I've done.
> >
> > Still needs some work ...
> >
> > One serious problem is that I do not think you can get away with
> reusing
> > typelem to link domains to base types.  All the array code is going
> to
> > think that a domain is an array, and proceed to do horribly wrong
> > things.  User applications may think the same thing, so even if you
> > wanted to change every backend routine that looks at typelem, it
> > wouldn't be enough.  I think the only safe way to proceed is to add
> a
> > separate column that links a domain to its base type.  This'd also
> save
> > you from having to add another meaning to typtype (since a domain
> could
> > be recognized by nonzero typbasetype).  That should reduce the
> > likelihood of breaking existing code, and perhaps make life simpler
> when
> > it comes time to allow freestanding composite types (why shouldn't a
> > domain have a composite type as base?).
> >
> > Come to think of it, even without freestanding composite types it'd
> be
> > possible to try to define a domain as a subtype of a composite type,
> > and to use same as (eg) a function argument or result type.  I doubt
> > you are anywhere near making that behave reasonably, though.  Might
> be
> > best to disallow it for now.
> >
> > Speaking of arrays --- have you thought about arrays of domain-type
> > objects?  I'm not sure whether any of the supported features matter
> for
> > array elements, but if they do it's not clear how to make it happen.
> >
> > Another objection is the changes you made in execMain.c.  That extra
> > syscache lookup for every field of every tuple is going to be a
> rather
> > nasty performance hit, especially seeing that people will pay it
> whether
> > they ever heard of domains or not.  And it seems quite unnecessary;
> if
> > you copy the domain's notnull bit into the pg_attribute row, then
> the
> > existing coding will do fine, no?
> >
> > I think also that you may have created some subtle changes in the
> > semantics of type default-value specifications; we'll need to think
> > if any compatibility problems have been introduced.  There are
> doubtless
> > hardly any people using the feature, so this is not a serious
> objection,
> > but if any change has occurred it should be documented.
> >
> >
> > Overall, an impressive first cut!
> >
> > regards, tom lane
> >

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