Embodiments relate to data processing. A method includes analyzing a plurality of data items in a relational database, where different portions of the data items are stored in a plurality of servers. The method also includes determining a maximum size of a subset of the data items stored in each of at least two servers among the plurality of servers, calculating a logarithm function based on the maximum size of the subset of the data items in each of the two servers, and calculating a highest number of sequences of communications between the two servers such that when the logarithmic function is iteratively applied, a value of the logarithmic function remains smaller than one. A protocol is then generated between the two servers for performing an intersection operation using the highest number of sequences calculated.