Re: Large expressions in indexes can't be stored (non-TOASTable)

On Thu, Oct 31, 2024 at 08:45:15AM +0900, Michael Paquier wrote:
> On Wed, Oct 30, 2024 at 03:54:32PM -0500, Nathan Bossart wrote:
>> I'll manage. 0001 was a doozy to back-patch, and this obviously isn't a
>> terribly pressing issue, so I plan to wait until after the November minor
>> release to apply this.
>
> Okay by me.

I took another look at 0001, and I think it still needs a bit of work.
Specifically, IIUC a few of these code paths are actually fine since they
do not ever touch a varlena column. For example,
clear_subscription_skip_lsn() only updates subskiplsn, so unless I am
missing a corner case, there is no risk of trying to access a TOAST table
without a snapshot. Allowing such cases would involve adjusting the new
assertions in 0003 to check for only the varlena columns during
inserts/updates, which is more complicated but seems doable.

Or we could just enforce that you have an active snapshot whenever you
modify a catalog with a TOAST table. That's simpler, but it requires extra
work in some paths (and probably comments to point out that we're only
pushing an active snapshot to satisfy an assertion).

>> I'm having second thoughts on 0002, so I'll
>> probably leave that one uncommitted, but IMHO we definitely need 0003 to
>> prevent this issue from reoccurring.
>
> I liked your idea behind 0002, FWIW. We do that for a lot of fields
> already in a Relation.

Alright, then I'll plan on proceeding with it.

--
nathan