Concurrent Subscriptions

With Concurrent Subscriptions, multiple data subscription workers can connect to the same subscription task simultaneously.
Each worker is assigned a different batch of documents to process.
By processing different batches in parallel, multiple workers can significantly accelerate the consumption of the subscription's contents.
Documents that were assigned to workers whose connection has ended unexpectedly,
can be reassigned by the server to available workers. See connection failure below.
In this page:

Defining concurrent workers

Concurrent workers are defined similarly to other workers, except their strategy is set to 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
  }
});

Dropping a connection

Use Subscriptions.DropSubscriptionWorker to forcefully disconnect the specified 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);

Connection failure

When a concurrent worker's connection ends unexpectedly, the server may reassign 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 was processing before the disconnection.
As a result, documents may be processed more than once:
- first by a worker that disconnected unexpectedly without acknowledging the completion of its assigned documents,
- and later by other workers the documents are reassigned to.

Defining concurrent workers​

Dropping a connection​

Connection failure​

Defining concurrent workers

Dropping a connection

Connection failure