1. An information processing method performed in a server computer communicably connected to a client computer, the server computer having a first execution environment and a second execution environment for executing a program for performing information processing in accordance with a series of processing requests transmitted from the client computer, the information processing method comprising steps of: storing a condition for judging whether a predetermined processing efficiency is assured for the information processing performed by the first execution environment according to the processing requests; receiving the series of processing requests transmitted from the client computer; judging whether the predetermined processing efficiency is assured according to the condition; allocating a predetermined processing request of the series of processing requests to the first execution environment when it is judged that the predetermined efficiency is assured with the first execution environment according to the condition; storing a session identifier identifying a series of sessions to which the predetermined processing request allocated to the first execution environment belongs therein; and when the server computer judges that the predetermined processing efficiency cannot be assured with the first execution environment according to the condition, storing data inherited between the series of processing requests, in a storage area accessible from the first execution environment and the second execution environment, and judging whether the session identifier identifying the session to which the processing request received from the client is stored; and when the session identifier is stored, a preventing the predetermined processing request from being allocated to the second execution environment; and storing the predetermined processing request not allocated to the second execution environment, as a wait request, and when the session identifier identifying the session, to which the wait request belongs, is attached to a response from the first execution environment, allocating the wait request to the second execution environment.