Re: Using MyDatabaseId in SET_LOCKTAG_APPLY_TRANSACTION

On Wed, 3 Dec 2025 at 12:38, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:

>
> Even with 64-bit XIDs, you can't have transactions older than 2^31 still
> running, right? So AFAICS you can continue using 32-bit XID in LOCKTAG.
>
>
Actually, I can, and some brave people do just that. Although it is bad
for a number of reasons. The issue is that I can't put on the same page
tuples with XIDs that differ by more than 2^31 using the current design
(with storing the XIDs "base" on the page). That is why I start thinking
about "real" 64-bit XIDs.

As for my original question, I think, the reason to have MyDatabaseId
in the LOCKTAG is that it's cheaper to store it in the lock, than try to
get it "on demand" in pg_lock_status() call by invoking
GetSubscription().

--
Best regards,
Maxim Orlov.