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

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Andrew Dunstan <andrew(at)dunslane(dot)net>
Cc: Tom Dunstan <pgsql(at)tomd(dot)cc>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Brendan Jurd <direvus(at)gmail(dot)com>, Bruce Momjian <momjian(at)postgresql(dot)org>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Re: [COMMITTERS] pgsql: Update: < * Allow addingenumerated values to an existing
Date: 2008-04-26 13:44:23
Message-ID: 20080426134423.GD10366@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers
Andrew Dunstan escribió:

> Tom Dunstan wrote:
>> So two alternative proposals, both with a 2 byte "enum id" and a 2 byte "value":
>>
>> 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.
>
> Or else we just error out in such cases. As Tom Lane suggests, rewriting  
> has some nasty deadlock possibilities.
>
> You always have the option of creating a new enum type and moving each  
> affected column to that type.

Another alternative would be internally creating a different temporary
enum, rewriting the tables one by one each on its own transaction, and
finish by dropping the original enum and renaming the temporary one.
This solves the deadlock problem.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

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