This. But if you use integer surrogate primary keys and seed one server with even ones and one server with odd ones, both incrementing by two, and put some uniq

This. But if you use integer surrogate primary keys and seed one server with even ones and one server with odd ones, both incrementing by two, and put some uniqueness constraint on your natural key, you won't have this issue of insert collisions and halted replication, just normal SQL errors. IIRC (non postgres-based advice from an earlier life but should work.)