What is the difference between push-based and pull-based streaming?

Push-based and pull-based streaming are two approaches for handling data flow between servers and clients. In push-based streaming, the server proactively sends data to clients as soon as it becomes available, without requiring explicit requests. This is common in real-time systems like live video streaming or chat applications, where immediacy is critical. For example, in a sports score app, the server pushes score updates to all connected clients the moment a goal is scored. In contrast, pull-based streaming relies on clients repeatedly asking the server for new data at fixed intervals. This approach is often used in scenarios where real-time updates are less critical, such as fetching daily weather reports or checking for system logs. Here, clients control the timing of data retrieval, like a mobile app polling an API every 5 minutes for new notifications.

The choice between push and pull often depends on use-case requirements. Push-based systems excel in low-latency scenarios, where delays are unacceptable. For instance, financial trading platforms use push models to broadcast stock price changes instantly to traders. However, this requires servers to maintain open connections with clients, which can strain resources when scaling to millions of users. Pull-based systems, while simpler to implement, introduce trade-offs. A client checking a backend service hourly for software updates might miss critical patches until the next poll. Pull models reduce server load since connections are transient, but they risk serving stale data if the polling interval is too long. Hybrid approaches, like HTTP long polling, combine aspects of both: clients initiate requests, but servers hold the connection open until new data is ready to “push,” balancing responsiveness and resource efficiency.

Technical considerations also differ. Push-based streaming typically relies on protocols like WebSockets or Server-Sent Events (SSE), which maintain persistent connections. These require careful handling of network interruptions—for example, reconnecting a dropped WebSocket in a live video feed. Pull-based systems often use standard REST APIs or HTTP endpoints, making them easier to cache (e.g., using CDNs for static content). However, frequent polling can lead to unnecessary network traffic, especially if data rarely changes. Developers must weigh factors like latency tolerance, scalability needs, and infrastructure complexity. For instance, a real-time collaborative document editor needs push to sync edits instantly, while a blog platform might opt for pull to serve articles with minimal backend overhead. The decision ultimately hinges on balancing real-time requirements against system constraints.