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Event batching for the C# SDK

The Optimizely Feature Experimentation C# SDK uses the event processor to batch decisions and conversion events into a single payload before sending it.

The C# SDK lets you batch events and includes options to set an event batch size, event time interval and event flush interval. The benefit of event batching is less network traffic for the same number of impression and conversion events tracked.

In the C# SDK, BatchEventProcessor provides the implementation of the EventProcessor interface and batches events. You can control batching based on two parameters:

  • Batch size – Defines the number of batched events before sending to Optimizely Feature Experimentation.
  • Flush interval – Defines the amount of time after which any batched events should be sent to Optimizely Feature Experimentation.

An event consisting of the batched payload is sent as soon as the batch size reaches the specified limit or the flush interval reaches the specified time limit. BatchEventProcessor options are described in the following sections.



Event batching works with both out-of-the-box and custom event dispatchers.

The event batching process does not remove any personally identifiable information (PII) from events. You must still ensure that you are not sending any unnecessary PII to Optimizely Feature Experimentation.

Basic example

using OptimizelySDK;

public static class Program
   public static void Main(string[] args)
        var sdkKey = args[0];
        // Returns Optimizely Client

By default, the batch size is 10 and the flush interval is 30 seconds.

Advanced example

using OptimizelySDK;
using OptimizelySDK.Config;
using OptimizelySDK.Event;

public static class Program
    public static void Main(string[] args)
        var sdkKey = args[0];
        var projectConfigManager = HttpProjectConfigManager.Builder()

        var batchEventProcessor = new BatchEventProcessor.Builder()

        var optimizely = new Optimizely(
            configManager: projectConfigManager,
            // ... Other parameters
            eventProcessor: batchEventProcessor



The maximum payload size is 3.5 MB. Optimizely rejects requests with a 400 response code, Bad Request Error, if the batch payload exceeds this limit.

The size limitation is because of the Optimizely Events API, which Feature Experimentation uses to send data to Optimizely.

The most common cause of a large payload size is a high batch size. If your payloads exceed the size limit, try configuring a smaller batch size.


BatchEventProcessor is an implementation of EventProcessor where events are batched. The class maintains a single consumer thread that pulls events off of the BlockingCollection and buffers them for either a configured batch size or a maximum duration before the resulting LogEvent is sent to the EventDispatcher and NotificationCenter.

The following properties can be used to customize the BatchEventProcessor configuration using the Builder class

PropertyDefault valueDescription
EventDispatcherDefautEventDispatcherUsed to dispatch event payload to Optimizely Feature Experimentation.
BatchSize10The maximum number of events to batch before dispatching. Once this number is reached, all queued events are flushed and sent to Optimizely Feature Experimentation.
FlushInterval30000 (30 Seconds)Milliseconds to wait before batching and dispatching events.
EventQueue1000BlockingCollection that queues individual events to be batched and dispatched by the executor.
NotificationCenternullNotification center instance to be used to trigger any notifications.

For more information, see Initialize the C# SDK.

Side effects

The table lists other Optimizely Feature Experimentation functionality that may be triggered by using this class.

LogEvent (see following section)Whenever the event processor produces a batch of events, a LogEvent object will be created using the EventFactory.

It contains batch of conversion and decision events.

This object will be dispatched using the provided event dispatcher and also it will be sent to the notification subscribers.
Notification ListenersFlush invokes the LOGEVENT notification listener if this listener is subscribed to.

Register LogEvent listener

To register a LogEvent listener:

    new NotificationCenter.LogEventCallback((logevent) => {
        // Your code here


LogEvent object gets created using EventFactory. It represents the batch of decision and conversion events we send to the Optimizely Feature Experimentation backend.

string URL to dispatch log event to.
Dictionary<string, object>Parameters to be set in the log event. It contains EventBatch of all UserEvents inside Visitors.
stringThe HTTP verb to use when dispatching the log event. It can be GET or POST.
Headers Dictionary<string, string> HeadersHeaders to be set when sending the request.

Dispose Optimizely Feature Experimentation on application exit

If you enable event batching, you must call the Close method (optimizely.Dispose()) before exiting. This ensures that queued events are flushed as soon as possible to avoid data loss.


Because the Optimizely Feature Experimentation client maintains a buffer of queued events, you must call Dispose() on the instance before shutting down your application or whenever dereferencing the instance.

Dispose()Stops all timers and flushes the event queue. This method will also stop any timers that are happening for the data-file manager.