Re: Make use of unvolatize() in vac_truncate_clog()

On 25.02.26 18:49, Bertrand Drouvot wrote:
> Hi,
>
> On Wed, Feb 25, 2026 at 02:33:29PM +0100, Peter Eisentraut wrote:
>> On 24.02.26 19:16, Bertrand Drouvot wrote:
>>> On Tue, Feb 24, 2026 at 11:19:50AM -0600, Nathan Bossart wrote:
>>>> On Tue, Feb 24, 2026 at 05:08:09PM +0000, Bertrand Drouvot wrote:
>>>>> This patch makes use of unvolatize() in vac_truncate_clog().
>>>>>
>>>>> Note that it does not remove the warning but moves it to c.h (where unvolatize()
>>>>> is defined) but that's consistent with what 481018f2804 did too.
>>>>
>>>> Why is this preferable to marking the function parameter as volatile
>>>
>>> I think that that would sound misleading for the other callers that don't really
>>> need the volatile qualification.
>>>
>>>> or removing the volatile qualifier from the variable?
>>>
>>> That looks mandatory according to 2d2e40e3bef.
>>
>> Arguably, putting the volatile qualifier on the whole dbform is broader than
>> required. So you could imagine writing it something like this instead:
>>
>> FormData_pg_database *dbform = (Form_pg_database) GETSTRUCT(tuple);
>> volatile TransactionId *datfrozenxid_p;
>> volatile TransactionId *datminmxid_p;
>>
>> *datfrozenxid_p = dbform->datfrozenxid;
>> *datminmxid_p = dbform->datminmxid;
>
> I think that looks like the best option as it also removes completely the
> volatile qual warning.
>
> That's done that way in 0001 (also moving back from FormData_pg_database to
> Form_pg_database as pre 2d2e40e3bef).
>
> Also, I'm using the same pattern in 0002 for vac_update_datfrozenxid() as
> f65ab862e3b:
>
> - was fixing the same kind of race as 2d2e40e3bef was fixing
> - added a comment for vac_update_datfrozenxid() mentioning the race in
> vac_truncate_clog(). So that's better if they both use the same pattern.

Committed (squashed into one patch)