The KOM Archive functionality enables the D2000 KOM process to work in the offline mode (no connection to the D2000 Server process) and to save values acquired from communication into a file (archive) for their later transmission into the D2000 system.
This functionality enables a remotely running D2000 KOM process to avoid losses of communication data :
- in case of network disruption between the D2000 KOM and the D2000 Server processes
- in case of failure of the D2000 Server process or the entire application server
- in case of D2000 upgrade
The KOM Archive functionality for the D2000 KOM process is activated by /KA<ArchivSize> and /KX command line parameters. The /KA parameter enables the KOM Archive functionality and the parameter ArchivSize is the size of the archive file in megabytes (between 1 and 400). The /KX parameter enables the operation of the D2000 KOM process after a loss of communication with the D2000 Server. An optional parameter /KM defines the method for sending values from the KOM archive after connection with the D2000 Server is established.
The D2000 KOM process with the KOM Archive functionality can be also started without the D2000 Server process. In that case, the configuration is read from a file, that is placed in the subdirectory \KOMARC of the application directory. The subdirectory is created automatically after running the D2000 KOM process with the parameter /KA. Besides the above-mentioned parameters, there is also the /KC<ApplicationName> parameter required for the definition of the location of the configuration file.
A necessary condition to run the D2000 KOM process without the D2000 Server process is the existence of the configuration file. The file is created and updated automatically after the D2000 KOM process is connected to the D2000 Server process. The file is updated after each change of child objects (lines, stations, I/O tags) that belong to a specific D2000 KOM process.
Use of KOM Archive in redundant systems:
Communication between D2000 KOM processes in redundant systems has not yet been implemented, so their use is limited. The D2000 KOM process, which starts without the D2000 Server process, is automatically HOT (i.e. there is a possibility of a collision of several HOT D2000 KOM processes).
A partial solution (working while at least one D2000 Server process is in the system) is to run the D2000 KOM process in the "shadow" mode (the parameters /RD<GroupName> and /W<MyName>,<MyNumber>)
KOM nr.1: kom /RDmy_group /Wself,1 /KCmy_application /KX /KA100 /TP
KOM nr.2: kom /RDmy_group /Wself,2 /KCmy_application /KX /KA100 /TP
The D2000 KOM processes started in this way are connecting to the HOT server. One of them is active and the other one is passive - it acts as if it was connected to the STANDBY D2000 Server. After the current D2000 Server becomes unavailable or STANDBY, the D2000 KOM processes attempt to connect to a new HOT server. When all servers are unavailable, the D2000 KOM processes stay in the same state as they were before the D2000 Server became unavailable (one is active and the other one is passive).
A problem can occur, when something happens to the active D2000 KOM process (the other D2000 KOM process is not notified and stays in the STANDBY state till it is reconnected to the D2000 Server).
Another problem is starting the D2000 KOM process when no server exists - the D2000 KOM process is automatically transferred into the active state as mentioned above.