Re: lastOverflowedXid does not handle transaction ID wraparound

On Wed, Oct 20, 2021 at 9:01 PM Kyotaro Horiguchi
<horikyota.ntt@gmail.com> wrote:
>
> lastOverflowedXid is the smallest subxid that possibly exists but
> possiblly not known to the standby. So if all top-level transactions
> older than lastOverflowedXid end, that means that all the
> subtransactions in doubt are known to have been ended.

Thanks for the patch! I verified that it appears to reset
lastOverflowedXid properly.

I may not be understanding

https://github.com/postgres/postgres/blob/dc899146dbf0e1d23fb24155a5155826ddce34c9/src/backend/storage/ipc/procarray.c#L1326-L1327
correctly, but isn't lastOverflowedXid the last subxid for a given
top-level XID, so isn't it actually the largest subxid that possibly
exists?