Re: WIP: extensible enums

On 10/17/2010 05:30 AM, Dean Rasheed wrote:
> On 16 October 2010 18:25, Dean Rasheed<dean(dot)a(dot)rasheed(at)gmail(dot)com> wrote:
>> Are there corner cases the author has failed to consider?
>>
>> None that I could find.
>>
>> Are there any assertion failures or crashes?
>>
> I just thought of another corner case, which can lead to a crash. The
> comparison code assumes that the number of elements in the enumeration
> is constant during a query, but that's not necessarily the case. For
> example the following will crash it:
>
> CREATE TYPE test_enum AS ENUM('Elem 1');
>
> CREATE OR REPLACE FUNCTION test_fn(a int) RETURNS test_enum AS
> $$
> DECLARE
> new_label text;
> BEGIN
> new_label := 'Elem '||a;
> EXECUTE 'ALTER TYPE test_enum ADD '''||new_label||''' BEFORE ''Elem 1''';
> RETURN new_label::test_enum;
> END;
> $$
> LANGUAGE plpgsql;
>
> WITH t(a) AS (SELECT test_fn(i) FROM generate_series(2, 10) g(i))
> SELECT MAX(a) from t;
>
> Of course that's a pathalogical example, but we should protect against
> it, preferrably without compromising performance in more normal cases.

Yeah, good point. But how do we manage that? Looking up the number of
elements on each function call will cause a performance degradation, I
suspect. I'll think about it, but if you have any ideas please speak up.
I'm fairly sure we should also recheck the cached sorted property for
the same reason, incidentally.

cheers

andrew