Concurrent Subscriptions

Concurrent workers are defined similarly to other workers, except their strategy is set to Concurrent.

• To define a concurrent worker:

  • Create the worker using getSubscriptionWorker.
  • Pass it a subscription worker options object.
  • Set the strategy to Concurrent

• Usage:

  • Define two concurrent workers
    

    // Define 2 concurrent subscription workers
    // ========================================
    
    const options = {
        // Set concurrent strategy
        strategy: "Concurrent", 
        subscriptionName: "Get all orders",
        maxDocsPerBatch: 20
    };
    
    const worker1 = documentStore.subscriptions.getSubscriptionWorker(options);
    const worker2 = documentStore.subscriptions.getSubscriptionWorker(options);

  • Run both workers
    

    worker1.on("batch", (batch, callback) => {
        try {
            for (const item of batch.items) {
                // Process item
            }
            callback();
    
        } catch(err) {
            callback(err);
        }
    });
    
    worker2.on("batch", (batch, callback) => {
        try {
            for (const item of batch.items) {
                // Process item
            }
            callback();
    
        } catch(err) {
            callback(err);
        }
    });

• Use dropSubscriptionWorker to forcefully disconnect the specified worker from the subscription it is connected to.

• Use dropConnection to disconnect ALL workers connected to the specified subscription.

// Drop connection for worker2
await documentStore.subscriptions.dropSubscriptionWorker(worker2);

// Available overloads:
dropConnection(options);
dropConnection(options, database);
dropSubscriptionWorker(worker);
dropSubscriptionWorker(worker, database);

• 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.