[anarazel]

Not normally, no. A real snapshot is held during the initial creation of the logical slot. After that the slot's "catalog xmin" prevents old catalog (but not user table!) row versions from being removed, but that's somewhat different from a snapshot.

[jeltz]

Exactly. We had to disable some cron jobs which abuse temporary tables (and functions!) to avoid catalog bloat but there were no long lived snapshots on the master during the upgrade.