Techniques are described for reducing the number of transactions required to perform operations for services that support many-to-many relationships between entities. A one-to-many operation that involves an entity of a first type and multiple entities of a second type may be performed in two asynchronous phases: a one-to-intermediary phase and an intermediary-to-many phase. During the one-to-intermediary phase, a single transaction is performed between the entity of the first type and an intermediary. During the intermediary-to-many phase, a distinct transaction is performed between the intermediary and each of the entities of the second type that are involved in the one-to-many operation. The transaction performed for a particular entity of the second type during the intermediary-to-many phase may aggregate all changes that affect the particular entity, thereby significantly reducing the number of transactions performed by the system. The reduction in the number of transactions produces a variety of benefits, including both a reduction in computational overhead and a reduction in storage space consumption.