Data Subscriptions: Concurrent Subscriptions

Concurrent workers are defined similarly to other workers, except for their strategy that is set as SubscriptionOpeningStrategy.Concurrent.

• To define a concurrent worker:

  • Create the worker using GetSubscriptionWorker.
  • Pass it a SubscriptionWorkerOptions instance.
  • Set the strategy to SubscriptionOpeningStrategy.Concurrent.

• Usage:

  • Define two concurrent workers
    

    // Define concurrent subscription workers
    var subscriptionWorker1 = store.Subscriptions.GetSubscriptionWorker<Order>(
        // Set the worker to connect to the "All Orders" subscription task
        new SubscriptionWorkerOptions("All Orders")
        {
            // Set Concurrent strategy
            Strategy = SubscriptionOpeningStrategy.Concurrent,
            MaxDocsPerBatch = 20
        });
    
    var subscriptionWorker2 = store.Subscriptions.GetSubscriptionWorker<Order>(
        new SubscriptionWorkerOptions("All Orders")
        {
            Strategy = SubscriptionOpeningStrategy.Concurrent,
            MaxDocsPerBatch = 20
        });

  • Run both workers
    

    // Start the concurrent worker. Workers will connect concurrently to the "All Orders" subscription task.
    var subscriptionRuntimeTask1 = subscriptionWorker1.Run(batch =>
    {
        // process batch
        foreach (var item in batch.Items)
        {
            // process item
        }
    });
    
    var subscriptionRuntimeTask2 = subscriptionWorker2.Run(batch =>
    {
        // process batch
        foreach (var item in batch.Items)
        {
            // process item
        }
    });

• Use Subscriptions.DropSubscriptionWorker to forcefully disconnect any concurrent worker from the subscription it is connected to.
  

  public void DropSubscriptionWorker<T>(SubscriptionWorker<T> worker, string database = null)

• Usage:
  

  //drop a concurrent subscription worker
  store.Subscriptions.DropSubscriptionWorker(subscriptionWorker2);

• When a concurrent worker's connection ends unexpectedly, the server may assign the documents this worker has been processing to any other concurrent worker that is available.
• A worker that reconnects after a connection failure will be assigned a new batch of documents.
  It is not guaranteed that the new batch will contain the same documents this worker had been processing before disconnecting.
• It may therefore happen that documents will be processed more than once:
  • First by a worker that disconnected unexpectedly, without acknowledging the procession of its documents,
  • and then by workers the documents have been reassigned to.