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Retry Mechanism#

When interacting with the MES, it is common to see reference to number of retries. There are two types of retries, client side retries and server side retries.

When the retries are made by the client application, in this case Connect IoT, the retry is a new REST request and is only activated in the following conditions:

  • If the http message comes back with a database deadlock
  • If the http message refers to a data changed since last view, which means there is an entity collision and the context is no longer guaranteed
  • If the http message refers to a data changed by another user
  • If the REST request comes back with a 401 Unauthorized
  • If the REST request replies with an ECONNREFUSED

If the error does not match one of these conditions, the client side retry will not be activated. If for example, there is a problem with logic in the system where the track-in fails for a functional reason, the retry will not activate. These scenarios should be handled by the Controller logic.

For server side requests, Connect IoT often allows the user to call the server side retry (that is Execute Service Call task) in the form of a task input. Refer to the documentation regarding this retry for more information.