Results ranking with simultaneous searchee and searcher optimization

A system comprising:

• at least one processor;
• and
• at least one memory coupled to the at least one processor;
• wherein the at least one memory comprises instructions that, when executed by the at least one processor, are capable of causing the at least one processor to perform operations comprising:
• applying at least one machine learning model to features of a search query, features of a searcher user, features of a searchee content item, and features of a searchee user;
• producing, by the at least one machine learning model, a first outcome prediction that represents a probability of a first objective relating to engagement of the searcher user with a content item in an online system and a second outcome prediction that represents a probability of a second objective relating to engagement of the searchee user with the online system responsive to the engagement of the searcher user with the content item;
• applying a multi-objective optimization solver to the first objective, the second objective and an outcome prediction that is a combination of the first outcome prediction and the second outcome prediction;
• and
• by the multi-objective optimization solver, generating a serving function for a search engine based on the first objective, the second objective, and the outcome prediction.