Re: Re: [COMMITTERS] pgsql: Update: < * Allow adding enumerated values to an existing

"Tom Dunstan" <pgsql@tomd.cc> writes:
> 1 - We space the values out as evenly as we can across the 65000ish
> range and allow people to delete, insert and append, but not reorder.
> If they do the above gratuitously we might have to do a rewrite, but
> they'll have to get fairly busy to do it. Rewrite would be required
> for reorderings.

> 2- We totally give up the idea of storing a value on disk that is
> directly comparable (other than equality), and simply number from zero
> up, using that number to index into an array (or use as syscache key
> or whatever) containing the real ordering information. We can then
> reorder or do any other operations to our heart's content.

> I'm actually favouring option 2 -

I'm not ... it strikes me that it will add implementation complexity and
runtime overhead for a feature that two days ago we didn't think we
needed at all, and IMHO one we still shouldn't be thinking to expend a
lot of work on.

I like #1 with no rewrite support.  That strikes me as covering 99%
of the requirements with 10% of the work.

Further, as already noted, if you do have to rewrite then a series of
manual ALTER COLUMN TYPE operations would probably be a *better* answer
than a monolithic implementation, because of the locking problems
involved in doing it in one transaction.  (Oh, and don't forget the disk
space problem: double the disk space for every table involved,
simultaneously.)
        regards, tom lane

PS: no, I do *not* want to hear any proposals for ALTER TYPE
CONCURRENTLY ;-)