As the clown in a New Yorker cartoon once told his doctor, “It only hurts when I laugh on the outside and cry on the inside.” The librettist-composer Ruggero Leoncavallo would have sympathized. Canio, the unloved top banana in his imperishable Pagliacci, suffers from the same complaint, and so in her way does his Zazà, a diva of the music hall who falls hard for a four-flushing family man. A century ago, the opera to which she lends her name served as a Cadillac for divas of the first magnitude—Geraldine Farrar, for one, whose 23 performances with the Metropolitan Opera were the first and last in the company’s history. In Vienna’s long-overdue staging, Zazà is an all but blank slate for the talents of Svetlana Aksenova, who has been paying her dues as Tosca and Madama Butterfly (both signature roles of Farrar’s). —M.G.