Re: Disabling vacuum truncate for autovacuum

On Thu, Mar 20, 2025 at 09:59:45AM -0700, David G. Johnston wrote:
> I get the need for this kind of logic, since we used a boolean for the
> table option, but as a self-proclaimed hack it seems worth more comments
> than provided here. Especially pertaining to whether this is indeed
> generic or vacuum_truncate specific. It's unclear since both isset and
> vacuum_truncate_set have been introduced.

I'm happy to expand the comments, but...

> If it is now a general property
> applying to any setting then vacuum_truncate_set shouldn't be needed - we
> should just get the isset value of the existing vacuum_truncate reloption
> by name.

the reason I added this field is because I couldn't find any existing way
to get this information where it's needed. So, I followed the existing
pattern of adding an offset to something we can access. This can be used
for any reloption, but currently vacuum_truncate is the only one that does.

How does something like this look for the comment?

/*
* isset_offset is an optional offset of a field in the result struct
* that stores whether the value is explicitly set for the relation or
* has just picked up the default value. In most cases, this can be
* deduced by giving the reloption a special default value (e.g., -2 is
* a common one for integer reloptions), but this isn't always
* possible. One notable example is Boolean reloptions, where it's
* difficult to discern the source of the value. This offset is only
* used if given a value greater than zero.
*/
int isset_offset;

--
nathan