Re: per-column generic option

On Mon, Jul 11, 2011 at 12:11 AM, Alvaro Herrera
<alvherre@commandprompt.com> wrote:
> Excerpts from Robert Haas's message of dom jul 10 21:21:19 -0400 2011:
>> On Jul 9, 2011, at 10:49 PM, Alvaro Herrera <alvherre@commandprompt.com> wrote:
>> > In short: in my opinion, attoptions and attfdwoptions need to be one
>> > thing and the same.
>>
>> I feel the opposite. In particular, what happens when a future release of PostgreSQL adds an attoption that happens
tohave the same name as somebody's per-column FDW option?  Something breaks, that's what... 
>
> Hmm, if you follow my proposal above, that wouldn't actually happen,
> because the core options do not apply to foreign columns.

Well, not at the moment.  But I think it's altogether likely that we
might want them to in the future.  The foreign data wrapper support we
have right now is basically a stub until we get around to improving
it, so we don't (for example) analyze foreign tables, which means that
n_distinct is not relevant.  But that's something we presumably want
to change at some point.  Eventually, I would anticipate that we'll
have quite a few more column options and most will apply to both
tables and foreign tables, so I'm not keen to bake in something that
makes that potentially problematic.  I think we should understand
attoptions as things that modify the behavior of PostgreSQL, while
attfdw/genoptions are there solely for the foreign data wrapper to
use.  An extra nullable field in pg_attribute isn't costing us
anything non-trivial, and the syntactic and definitional clarity seems
entirely worth it.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company