Re: Alter or rename enum value

On 9 March 2016 at 20:19, Matthias Kurz <m(dot)kurz(at)irregular(dot)at> wrote:

> Besides not being able to rename enum values there are two other
> limitations regarding enums which would be nice to get finally fixed:
>
> 1) There is also no possibility to drop a value.
>
> 2) Quoting the docs (
> http://www.postgresql.org/docs/9.5/static/sql-altertype.html)
> "ALTER TYPE ... ADD VALUE (the form that adds a new value to an enum type)
> cannot be executed inside a transaction block." Example:
> # CREATE TYPE bogus AS ENUM('good');
> CREATE TYPE
> # BEGIN;
> BEGIN
> # ALTER TYPE bogus ADD VALUE 'bad';
> ERROR: ALTER TYPE ... ADD cannot run inside a transaction block
>
> To summarize it:
> For enums to finally be really usable it would nice if we would have (or
> similiar):
> ALTER TYPE name DROP VALUE [ IF EXISTS ] enum_value
> and
> ALTER TYPE name RENAME VALUE [ IF EXISTS ] old_enum_value_name TO
> new_enum_value_name
>
> And all of the operations (adding, renaming, dropping) should also work
> when done within a new transaction on an enum that existed before that
> transaction.
>
> I did some digging and maybe following commits are useful in this context:
> 7b90469b71761d240bf5efe3ad5bbd228429278e
> c9e2e2db5c2090a880028fd8c1debff474640f50
>
> Also there are these discussions where some of the messages contain some
> useful information:
>
> http://www.postgresql.org/message-id/29F36C7C98AB09499B1A209D48EAA615B7653DBC8A@mail2a.alliedtesting.com
> http://www.postgresql.org/message-id/50324F26.3090809@dunslane.net
>
> http://www.postgresql.org/message-id/20130819122938.GB8558@alap2.anarazel.de
>
> Also have a look at this workaround:
> http://en.dklab.ru/lib/dklab_postgresql_enum/
>
> How high is the chance that given the above information someone will
> tackle these 3 issues/requests in the near future? It seems there were some
> internal chances since the introduction of enums in 8.x so maybe this
> changes wouldn't be that disruptive anymore?
>
> Regards,
> Matthias
>
> On 9 March 2016 at 18:13, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
>> > On 03/09/2016 11:07 AM, Tom Lane wrote:
>> >> I have a vague recollection that we discussed this at the time the enum
>> >> stuff went in, and there are concurrency issues? Don't recall details
>> >> though.
>>
>> > Rings a vague bell, but should it be any worse than adding new labels?
>>
>> I think what I was recalling is the hazards discussed in the comments for
>> RenumberEnumType. However, the problem there is that a backend could make
>> inconsistent ordering decisions due to seeing two different pg_enum rows
>> under different snapshots. Updating a single row to change its name
>> doesn't seem to have a comparable hazard, and it wouldn't affect ordering
>> anyway. So it's probably no worse than any other object-rename situation.
>>
>> regards, tom lane
>>
>
>
Is there a way or a procedure we can go through to make the these ALTER
TYPE enhancements a higher priority? How do you choose which
features/enhancements to implement (next)?