What are some best practices for optimizing the performance and scalability of server sent events?

1 Choose the right use case

SSE are not a one-size-fits-all solution for every web application. They are best suited for scenarios where the server has frequent and small updates to send to the client, and where the client does not need to send data back to the server. For example, SSE are ideal for displaying live scores, weather, or notifications. On the other hand, SSE are not recommended for applications that require bidirectional communication, such as video conferencing, gaming, or file sharing. For those cases, WebSocket or WebRTC might be more appropriate.

2 Limit the number of connections

One of the main challenges of SSE is that they require a persistent HTTP connection between the server and the client. This means that the server has to maintain a large number of open connections, which can consume a lot of resources and affect the performance and scalability of the application. Therefore, it is important to limit the number of connections per server and per client. One way to do this is to use a proxy or a load balancer that can distribute the connections across multiple servers and handle the connection management. Another way is to use a service worker or a shared worker on the client side that can receive the SSE and broadcast them to other tabs or windows.

3 Optimize the data format and frequency

Another factor that can impact the performance and scalability of SSE is the amount and frequency of data that the server sends to the client. Sending too much or too often can overload the network and the browser, while sending too little or too rarely can result in stale or outdated data. Therefore, it is important to optimize the data format and frequency according to the needs and capabilities of the application. One way to do this is to use a binary or a compressed data format, such as JSON or Protobuf, that can reduce the size and bandwidth of the data. Another way is to use a throttling or a debouncing technique, that can limit the number and frequency of the data updates.

4 Handle errors and reconnects

SSE are not immune to errors and interruptions that can occur in the network or the server. For example, the connection can be dropped, timed out, or closed by the server or the client. In those cases, the client needs to handle the errors and reconnect to the server. Fortunately, SSE have a built-in mechanism that can automatically reconnect the client to the server after a specified interval. However, this mechanism can also cause some issues, such as duplicate or missing data, or excessive reconnection attempts. Therefore, it is important to handle the errors and reconnects properly and gracefully. One way to do this is to use a unique event ID that can identify each data update and prevent duplicates or gaps. Another way is to use a backoff strategy that can increase the reconnection interval progressively and avoid spamming the server.