Re: Adding a stored generated column without long-lived locks

Hi Laurenz,

thanks for your feedback!

On Mon Aug 24, 2026 at 7:29 PM CEST, Laurenz Albe wrote:
> On Thu, 2026-08-06 at 14:36 +0200, Alberto Piai wrote:
>> PFA v7, implementing this version of the command:
>>
>> ... ALTER col ADD GENERATED USING CONSTRAINT constr_name STORED
>
> Great! I think this is pretty much good to go.
>
>> In particular, all the error messages now follow the guidelines for
>> error reporting. I tried to use a consistent error message everywhere,
>> adding details and hints where appropriate.
>
> Much better!
>
> I was wondering about this hint:
>
> Use this command on the root table/partition without ONLY.
>
> You can never turn a column of a partition into a generated column, right?
> How about
>
> Use the command on the partition root without specifying ONLY.

Since this is also taking care of classic inheritance, it seems strange
to only mention partitions. But I see that this way it's confusing (and
I do concede that partitioning might be the more widely used of the two)
so I switched it around to "on the root partition/table without
specifying ONLY". Does that make more sense?

> This detail message is longer than 80 characters:
>
> Converting a column to a stored generated column can only be done on the whole hierarchy at once.
>
> How about
>
> Converting only part of a partitioning/inheritance hierarchy is not supported.

Much better, fixed.

> There is one sentence in the documentation that sounds wrong to me:
>
> + <para>
> + After this command is run, <literal>column_name</literal> will be a stored
> + generated column with <literal>expr</literal> as its generation
> + expression.
> + </para>
>
> Shouldn't it be "after this command has been run"? Or perhaps "has completed"?

Thanks, changed to "has completed".

The attached v8 addresses the points above.

Kind regards,

Alberto

--
Alberto Piai
Sensational AG
Zürich, Switzerland