Re: problems with toast.* reloptions

On Tue, Jun 24, 2025 at 02:10:55PM +0900, Michael Paquier wrote:
> On Mon, Jun 23, 2025 at 03:59:56PM -0500, Nathan Bossart wrote:
>> Here is a very rough proof-of-concept patch set for this. AFAICT there are
>> a few options we cannot fix on the back-branches because there is no way to
>> tell whether it is set or has just picked up the default. On v18 and
>> newer, we could use isset_offset, but that doesn't exist on older versions.
>> (I haven't looked closely, but I'm assuming that back-patching isset_offset
>> isn't an option.)
>
> Hmm. I am wondering if we need to be aggressive about this set of
> changes at all in the back branches. It's been broken for a long time
> without anybody really complaining about the fact that reloptions
> being set or not influenced the outcome in the context of autovacuum,
> so perhaps there is a good argument for keeping all that in v19. My
> conservative 2c.

Yeah, I'm tempted to even ask how folks feel about removing the toast.*
reloptions. Maybe there's some simple cases that work well enough, but
AFAICT any moderately-complicated setup basically doesn't work at all. In
any case, writing out this patch set has got me on the fix-on-HEAD-only
bandwagon.

>> I would like to explore the "option 2" from upthread [0] for v19. I think
>> that is a better long-term solution, and it may allow us to remove the
>> table_toast_map in autovacuum.
>
> It would be nice to have some tests here to check the state of the
> options used? My best guess would be a DEBUG1 entry combined with a
> scan of the logs generated and an aggressive autovacuum worker
> spawn to check that the options generated are what we expect for the
> relations autovacuum picks up.

Eh... I agree that's probably how we'd have to test it with the existing
tools, but it sure sounds like a recipe for a flaky test.

--
nathan