A communication system comprising computers and a management computer, wherein the computers include a communication control unit configured to control a communication using a session of a terminal. The communication control unit manages a database storing in a plurality of pieces of session information. The management computer includes property management information for managing a property of each of the plurality of pieces of session information. The session information migration control unit is configured to: detect a migration trigger of the plurality of pieces of session information stored in a first database; select the plurality of pieces of session information from the plurality of pieces of session information stored in the first database based on the property management information; determine a migration order for the selected plurality of pieces of session information based on the property of the each of the selected plurality of pieces of session information.