Applies To:
  • CitectSCADA 5.xx, 6.xx, 7.00
  • CitectHMI 5.xx, 6.xx, 7.00
Summary:
My display client seems to take a varying amount of time to swap over to a redundant server when one of the servers goes offline. Further, looking at the CitectSCADA Kernel statistics shown in the 'page table tran' window, I have seen that it shows a tran connection to a server that I know is offline (e.g. the remote server is switch off, citect is not running or the network is unplugged). However, the connection state is reported as "Online". Why is this so?  

Solution:
The reason is that client tran connections do not have a heartbeat that allows them to detect when a connection has been terminated. It is only whenever the client goes to use the tran connection, e.g. by making a request for data from a server, that it will work out that the connection is not available anymore, and set the state to 'Offline'. This issue will be seen most commonly with a connection to a Report server, as this type of server is generally contacted the least frequently.

Is this a problem? Other than showing potentially misleading statistics in the kernel, this should not be a problem, because only when the client needs some data will it attempt to utilise the tran connection, and when it sees it is offline, it will swap over to a redundant server (if one exists). This can give the impression that swap over time to redundant servers seems to vary - it does. It will depend on the configuration and state of your project. However, this mechanism should not impact the correct runtime operation of your project, and should be considered normal CitectSCADA behaviour.

 
Keywords:
tran connection incorrect misleading slow swap swapover  

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