I believe it's an old Yiddish freiloch (check spelling!) tune, played still- with lots of reeds, at weddings and celebratory gatherings. And the harmonies go minor-key when, "suddenly, the setting is strange..." The words are recent, but I forget who wrote them. The song was on the Hit Parade- probably the '40s, or at the latest, early '50s. As to the title of the old freiloch, I don't know that either- ask a Klezmer musician, I'd say.