Data Subscriptions: How to Consume a Data Subscription

Internal mechanism errors

Those errors occur during the normal server-client communication between the worker and the server.
If an unexpected error occurs, the worker will try to reconnect to the server. There are conditions in which the worker will cease its operation and will not try to reconnect:

• The subscription does not exist or was deleted
• Another worker took over the subscription (see connection strategy)
• The worker could not connect to any of the servers
• The worker could not receive the node in charge of the task (this can happen when there is no leader)
• Authorization exception
• Exception during connection establishment

User's batch processing logic unhandled exception

Example:

_ = workerWBatch.Run(x => throw new Exception());

If an exception is thrown, the worker will abort the current batch process. A worker can be configured to treat the thrown exception by either of the following two ways:

• By default, the worker will wrap the thrown exception with a SubscriberErrorException exception and rethrow it,
  terminating the subscription execution without acknowledging progress or retrying. The task returned by the Run function will be terminated with an erroneous state, throwing a SubscriberErrorException exception.

• If SubscriptionWorkerOptions's value IgnoreSubscriberErrors is set to true, the erroneous batch will get acknowledged without retrying and the next batches will continue processing.

Reconnecting

In the cases above, we described situations in which a worker will try to reconnect with the server. There are two key SubscriptionWorkerOptions fields controlling this state:

• TimeToWaitBeforeConnectionRetry - The time that the worker will 'sleep' before trying to reconnect.
• MaxErroneousPeriod - The maximum time in which the worker is allowed to be in an erroneous state. After that time passes, the worker will stop trying to reconnect.

Timing out

A worker will time out after losing its connectivity with the server for a given time period.

• The timeout period can be set using the ConnectionStreamTimeout option.
  E.g.

  var options = new SubscriptionWorkerOptions(subscriptionName);
  
  // Set the worker's timeout period
  options.ConnectionStreamTimeout = TimeSpan.FromSeconds(45);

• Default timeout period: 30 second
  

OnUnexpectedSubscriptionError

OnUnexpectedSubscriptionError is the event raised when a connection failure occurs between the subscription worker and the server and it throws an unexpected exception. When this occurs, the worker will automatically try to reconnect again. This event is useful for logging these unexpected exceptions.