From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "Tom Dunstan" <pgsql(at)tomd(dot)cc> |
Cc: | "Brendan Jurd" <direvus(at)gmail(dot)com>, "Alvaro Herrera" <alvherre(at)commandprompt(dot)com>, "Andrew Dunstan" <andrew(at)dunslane(dot)net>, "Bruce Momjian" <momjian(at)postgresql(dot)org>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Re: [COMMITTERS] pgsql: Update: < * Allow adding enumerated values to an existing |
Date: | 2008-04-25 21:21:25 |
Message-ID: | 660.1209158485@sss.pgh.pa.us |
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Lists: | pgsql-committers pgsql-hackers |
"Tom Dunstan" <pgsql(at)tomd(dot)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 ;-)
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