A GT.M program uses Global Directory to reference a global variable (gvn) or resource name for the object of a database lock operation (nref) residing on a remote node. When a file in the Global Directory specifies a remote node name that does not match the name of the node on which the process is running, GT.M maps the segment to a database file on the remote node using the GT.CM client. The two main components of GT.CM are:

The GT.CM client sends messages containing the operation type (SET, KILL, $ORDER, etc), and operation specific data (eg. gvn to be SET, or KILLed) to the GT.CM server through a communication channel over a network. The client generally waits for response from the server and initiates error processing based on the status contained in the response. The format of the messages exchanged between the server and client is as defined by the FIS-developed GNP protocol.

The Global Directory of the client specifies a GT.CM database segment by prefixing its file with an alphanumeric <node-name>, followed by a colon (":"). Client processes using this database must have an environment variable of the form "GTCM_<node-name>" to locate the server. This environment variable may contain either a port number alone, or a host name or address and a port number in the form "<host-name-or-address>:<port-number>" or the form "[<host-name-or-address>]:<port-number>", where the square-brackets ([])are part of the text. If the port number is specified alone, GT.CM uses the <node-name> as the host name; otherwise, it uses the <node-name> solely as an identifier to match the segment in the Global Directory, and it obtains the host name or address from the contents of the environment variable. If a host name is specified, and the server host has multiple addresses, GT.CM uses the system default.

  • Because the <node-name> is strictly alphanumeric, it cannot represent an IP address or qualified host name due to the need for a dot (".") separator. If you need to specify an IP address or qualified host name, select an alphanumeric <node-name> and specify the <host-name-or-address> in the GTCM_<node-name> variable.

  • Use the "[<host-name-or-address>]:<port-number>" form to specify an IPv6 address.

This section describes the starting up and shutting down procedure of GT.CM server.

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