I'm not completely sure I understand your comment, so pardon me if I misunderstand. I don't think a foreign data wrapper would fundamentally to be more efficien

I'm not completely sure I understand your comment, so pardon me if I misunderstand. I don't think a foreign data wrapper would fundamentally to be more efficient with whatever table is ~foreign~, especially for an OUTER JOIN? Unless you're basically implementing something similar to data-diff with an OUTER JOIN with FDW, which seems possible If you're doing in-database diffs, however, a join-based approach will likely outperform data-diff though. Ideally databases would have support a standard MERKLE TREE INDEX so we could get extremely fast comparisons.