iOS has a feature that suppresses or limits the display of push notifications when multiple notifications are sent in quick succession (often referred to as rate limiting or filtering). Specifically, how many notifications within what timeframe might trigger such suppression?
You may be confusing the more common cause of overflowing the notification queue for your app with rate limiting.
Rate limiting and further protective measures up to banning will kick in when APNs detects a pattern of abuse or errant behavior by the push servers that adversely affect the service.
The conditions under which APNs will start taking protective measures is not documented. If your worry is indeed getting into that situation, then you must be aware that you could be getting into that situation either on purpose or by mistake, and my recommendation is to do your best to not do that.
If you are asking about losing notifications because they were not delivered in a timely manner, that is indeed a common occurrence, and this is how it works:
APNs provides a storage queue of ONE notification per apns-topic (usually means per app, unless you have different types of notifications for the same app). If for some reason the notification cannot be delivered to the target device, it will be stored in this queue until it can be delivered.
If another notification is sent to the device before the first one can be delivered, then the second notification will overwrite the first one in the queue. And the first notification will be lost and not delivered.
A common reason for not being able to deliver the notification is the device could be offline, or could be on an unreliable connection that APNs cannot sustain a persistent connection to. A timeframe for this cannot be established as it depends on the device, its usage patterns, and its network connectivity. As a developer, you have no visibility or control of this situation.
The important point is that apps should never be designed expecting that every push notification will be received. This is not how APNs is intended to work; it is intended to inform the user or app that some event of interest has occurred. Apps are expected to work properly, albeit perhaps with degraded functionality, if push notifications are not received. The user can turn off push notifications or background app updates at any time, and of course push notifications will not be received if the device doesn’t have network connectivity.
Argun Tekant / DTS Engineer / Core Technologies
