Re: Add sanity check for duplicate enum values in GUC definitions

> On Dec 17, 2025, at 23:19, Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> Hi,
>
> On 2025-12-15 17:16:56 +0800, Chao Li wrote:
>> The motivation for this patch comes from my own experience. While working
>> on [1]. I added an enum-typed GUC and made a copy-and-paste mistake,
>> assigning the same numeric value to two different enum entries. This
>> resulted in confusing runtime behavior and cost me about an hour to track
>> down.
>
> I think this is something we explicitly do *not* want. It can make plenty
> sense to have enums with the same value assigned multiple times. And ending up
> with a list of exceptions doesn't strike me as a good use of time.

There is actually only one enum (“wal_compression”) having duplicate values if excluding hidden items. In my patch, hidden items have been ignored, so the white-list has only one entry.

>
> I just dont' believe this is a frequent enough issue to be worth in-core
> infrastructure, particularly in light of it sometimes being actually
> intentionally used.
>

I think copy-paste mistake is easy to make. I have done an enhancement for GUC, see [1], that also helps debugging against such errors. In the discussion, you can see that Alvaro echoed that he made the same mistake.

[1] https://www.postgresql.org/message-id/CAEoWx2%3DoP4LgHi771_OKhPPUS7B-CTqCs%3D%3DuQcNXWrwBoAm5Vg%40mail.gmail.com

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/