If you create a large-scale system using OpenTP1, the number of ports that TCP/IP manages may run short. To prevent this, this appendix describes how to restrict the number of ports that OpenTP1 uses.

To reduce the overhead of establishing connections, OpenTP1 maintains the connections that are established and reuses them for the communications between the same processes. When the number of maintained connections reaches the limit, connections will be disconnected if the processes that established the connections agree with each other. This is temporary closing.

The user can specify the following operands in the system common definition, the user service definition, and the user service default definition.

set ipc_sockctl_highwater=a,b
set ipc_sockctl_watchtime=length-of-time-to-wait-until-the-
sockets-are-reusable

a

Percentage of sockets at which temporary closing starts

b

Percentage of sockets for which temporary closing is not performed

• Specifying the percentage of sockets at which temporary closing starts
  OpenTP1 starts temporary closing when the number of file descriptors used for the sockets in the process exceeds the following value:
  Value specified in the max_socket_descriptors operand (Value a specified in the ipc_sockctl_highwater operand/100)
  
• Specifying the percentage of sockets for which temporary closing is not performed
  You can specify the percentage of the number of connections that are not temporarily closed. Calculate the number of connections that are not temporarily closed as follows:
  Value specified in the max_socket_descriptors operand (Value b specified in the ipc_sockctl_highwater operand/100)
  
• Specifying the length of time to wait until the sockets are reusable
  In the ipc_sockctl_watchtime operand, specify the length of time (seconds) to wait from the moment the number of file descriptors used for the sockets in the process reaches the value specified in the max_socket_descriptors operand until the sockets become reusable due to temporary closing.
  

In the operation where communications between the same processes are infrequent or in a system that communicates with many remote processes, use temporary closing and release some connections when the number of maintained connections becomes great. This allows you to adjust the number of sockets that are used in a process and reuse the sockets.

When an OpenTP1 process sends data, it secures a send port before it establishes a connection. Since each computer has a limited number of send ports, you need to adjust the number of connections maintained by the UAP processes. Make this adjustment so the total number of send ports in the entire system does not exceed its limit.

If the values specified in these operands are inadequate, the number of sockets that can be used in a process reaches the upper limit. This causes new requests for establishing connections to overwhelm the number of sockets that become reusable by temporary closing. Alternatively, the process may terminate abnormally since the number of ports used in the entire system exceeds the limit of TCP/IP.