Re: Using MyDatabaseId in SET_LOCKTAG_APPLY_TRANSACTION

On 27/11/2025 18:00, Maxim Orlov wrote:
> Hi!
>
> While working on a patch to implement 64-bit transaction IDs in
> PostgreSQL, I ran into a small problem. The
> LockApplyTransactionForSession/UnlockApplyTransactionForSession
> functions utilize the SET_LOCKTAG_APPLY_TRANSACTION macro, which
> assumes XIDs are 32-bits.
>
> In my case, the transaction IDs are growing twice as large, and we don't
> have enough space to store them. I could simply resize the LOCKTAG
> structure, extending it by 32 bits, but this is not the best solution.
>
> However, I noticed that the MyDatabaseId field in
> SET_LOCKTAG_APPLY_TRANSACTION appears unnecessary. As far as I
> understand, the suboid should already uniquely identify the
> subscription. Is the MyDatabaseId field truly necessary? Will only the
> suboid suffice? I would be pleased to hear your thoughts on this.

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.

- Heikki