Event batching for the Android SDK

12 min

The Android 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 Android 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 passed to the Event Dispatcher to be sent to Optimizely.

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

Note The default Event Dispatcher in the Android SDK uses an Android Intent Service to dispatch batched requests. As a result you may observe additional delays to outbound requests beyond your specified flush interval as a result of system limits on those requests.

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.

Basic example

val optimizelyManager = OptimizelyManager.builder()
         .withSDKKey("<Your_SDK_Key>")
         .build(context)
val optimizely = optimizelyManager.initialize(context, R.raw.datafile)

OptimizelyManager optimizelyManager = OptimizelyManager.builder()
        .withSDKKey("<Your_SDK_Key>")
        .build(context);
OptimizelyClient optimizely = optimizelyManager.initialize(context, R.raw.datafile);

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

Advanced Example

val eventHandler: EventHandler = DefaultEventHandler.getInstance(context)

// Here we are using the builder options to set batch size
// to 5 events and flush interval to a minute.
val batchProcessor = BatchEventProcessor.builder()
         .withBatchSize(5)
         .withEventHandler(eventHandler)
         .withFlushInterval(TimeUnit.MINUTES.toMillis(1L))
         .build()
val optimizelyManager = OptimizelyManager.builder()
         .withSDKKey("<Your_SDK_Key>")
         .withEventHandler(eventHandler)
         .withDatafileDownloadInterval(15, TimeUnit.MINUTES)
         .withEventProcessor(batchProcessor)
         .build(context)
val optimizely = optimizelyManager.initialize(context, R.raw.datafile)

EventHandler eventHandler = DefaultEventHandler.getInstance(context);

// Here we are using the builder options to set batch size
// to 5 events and flush interval to a minute.
BatchEventProcessor batchProcessor = BatchEventProcessor.builder()
         .withBatchSize(5)
         .withEventHandler(eventHandler)
         .withFlushInterval(TimeUnit.MINUTES.toMillis(1L))
         .build();

OptimizelyManager optimizelyManager = OptimizelyManager.builder()
         .withSDKKey("<Your_SDK_Key>")
         .withEventHandler(eventHandler)
         .withDatafileDownloadInterval(15, TimeUnit.MINUTES)
         .withEventProcessor(batchProcessor)
         .build(context);

OptimizelyClient optimizely = optimizelyManager.initialize(context, R.raw.datafile);

Warning 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 is used 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

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.

Builder methods

Use the following methods to customize the BatchEventProcessor.

Property	Default value	Description
withEventHandler	null	Required field. Specifies event handler to use to dispatch event payload to Optimizely. By default, if you create an Optimizely instance, it passes in `AsyncEventHandler` to `BatchEventProcessor`.
withBatchSize	10	The maximum number of events to batch before dispatching. Once this number is reached, all queued events are flushed and sent to Optimizely.
withFlushInterval	30000 (30 Seconds)	Maximum time after which to batch and send event payload to Optimizely. In milliseconds.
withEventQueue	1000	BlockingCollection that queues individual events to be batched and dispatched by the executor.
withNotificationCenter	null	Notification center instance to be used to trigger any notifications to notify when event batches are flushed.
withExecutor	Single Thread Executor	Executor service that takes care of triggering event batching and subsequent dispatching to Optimizely.
withTimeout	5000	Maximum time to wait for event processor’s close to be executed. In milliseconds.

Advanced configuration

You can set the following properties to override the default configuration for BatchEventProcessor.

Property	Default value	Description
event.processor.batch.size	10	Maximum size of batch of events to send to Optimizely.
event.processor.batch.interval	30000	Maximum time after which to batch and send event payload to Optimizely. In milliseconds.
event.processor.close.timeout	5000	Maximum time to wait for event processor’s close to be executed. In milliseconds.

For information, see Initialize the Android SDK.

Side effects

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

Functionality	Description
`LogEvent`	Whenever the event processor produces a batch of events, a `LogEvent` object is created using the `EventFactory`. It contains batch of conversion and decision events. This object is dispatched using the provided event dispatcher and also it is sent to the notification subscribers
Notification Listeners	Flush invokes the LOGEVENT [notification listener](https://docs.developers.optimizely.com/feature-experimentation/docs/set-up-notification-listener-android) if this listener is subscribed to.

Register LogEvent listener

To register a LogEvent notification listener:

optimizely.notificationCenter?.addNotificationHandler(LogEvent::class.java) { logEvent: LogEvent ->
    Log.d("Optimizely", "event dispatched: $logEvent")
}

optimizely.getNotificationCenter().addNotificationHandler(LogEvent.class, logEvent -> {
    Log.d("Optimizely", "event dispatched: " + logEvent);
});

LogEvent

LogEvent object gets created using EventFactory. It represents the batch of decision and conversion events Optimizely sends to the Optimizely backend.

Object	Type	Description
requestMethod Required (non null)	RequestMethod (Enum)	The HTTP verb to use when dispatching the log event. It can be `GET` or `POST`.
endpointUrl\ Required (non null)	String	URL to dispatch log event to.
requestParams\ Required (non null)	Map\	Parameters to be set in the log event.
[eventBatch](https://github.com/optimizely/java-sdk/blob/13c27ffc812928ef5cf05159d37ad6bab421fc5a/core-api/src/main/java/com/optimizely/ab/event/LogEvent.java#L38)\ Required	EventBatch	It contains all the information regarding every event which is batched, including a list of visitors which contains UserEvent.

Close Optimizely on application exit

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

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

Method	Description
close()	Stops all executor threads and flushes the event queue. This method will also stop any scheduledExecutorService running for the data-file manager.