Re: BUG #14825: enum type: unsafe use?

On 09/22/2017 05:46 PM, Tom Lane wrote:
> balazs(at)obiserver(dot)hu writes:
>> PostgreSQL version: 10beta4
>> testdb=# begin;
>> BEGIN
>> testdb=# create type enumtype as enum ('v1', 'v2');
>> CREATE TYPE
>> testdb=# alter type enumtype owner to testrole;
>> ALTER TYPE
>> testdb=# create table testtable (enumcolumn enumtype not null default 'v1');
>> ERROR: unsafe use of new value "v1" of enum type enumtype
>> HINT: New enum values must be committed before they can be used.
> Hmm, that's pretty annoying. It's happening be

> cause check_safe_enum_use
> insists that the enum's pg_type entry not be updated-in-transaction.
> We thought that the new rules instituted by 15bc038f9 would be generally
> more convenient to use than the old ones --- but this example shows
> that, for example, pg_dump scripts involving enums often could not
> be restored inside a single transaction.
>
> I'm not sure if that qualifies as a stop-ship problem, but it ain't
> good, for sure. We need to look at whether we should revert 15bc038f9
> or somehow revise its rules.

:-(

The only real problem comes from adding a value to an enum that has been
created in an earlier transaction and then using that enum value. What
we're doing here is essentially a heuristic test for that condition, and
we're getting some false positives. I wonder if we wouldn't be better
doing this more directly, keeping a per-transaction hash of unsafe enum
values (which will almost always be empty). It might even speed up the
check.

cheers

andrew

--
Andrew Dunstan https://www.2ndQuadrant.com
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