Polling in software architecture, different types of polling, advantages, disadvantages, where to use and where not to use polling.

Polling in software architecture refers to the process of regularly checking the state or availability of a resource or condition to determine if a specific action should be taken. It is a common mechanism used in various software systems to obtain or monitor information from external sources, such as sensors, APIs, or databases. Polling is particularly useful when a system needs to keep track of changes or updates in an asynchronous manner.

There are different types of polling, each with its own advantages and disadvantages:

1. Regular Polling (Periodic Polling):

Advantages:

• Simplicity: It is straightforward to implement and understand.
• Predictable: You can control when the checks occur at fixed intervals.
• Low network overhead: It minimizes the constant need for communication.

Disadvantages:

• Inefficiency: If the polling interval is too short, it can lead to high resource usage.
• Latency: Polling may not be real-time, and there can be delays in receiving updates.
• Increased server load: Frequent polls can strain servers and networks.

Use Cases: Regular polling is suitable when real-time data is not critical, and a slight delay is acceptable, or when the server/resource being polled can handle the load without performance issues.

2. Long Polling (Comet or Hanging GET):

Advantages:

• Reduced latency: Allows the server to respond immediately when new data is available.
• Minimizes server load: Reduces the number of requests compared to regular polling.
• Suitable for real-time applications.

Disadvantages:

• Complex server-side implementation.
• Potential connection timeouts and re-establishment overhead.

Use Cases: Long polling is useful for real-time applications like chat services or collaborative tools where low latency is critical.

3. Server-Sent Events (SSE):

Advantages:

• Real-time updates: Provides a continuous stream of updates from the server.
• Simplicity: Easier to implement than WebSockets.
• No need for frequent reconnections.

Disadvantages:

• Limited browser support (not suitable for all clients).
• Unidirectional communication (server to client only).

Use Cases: SSE is ideal for applications that require real-time updates in a unidirectional manner, such as news feeds or live scoreboards.

4. WebSockets:

Advantages:

• Full-duplex communication: Allows bi-directional data exchange in real-time.
• Low latency and reduced network overhead.
• Suitable for a wide range of real-time applications.

Disadvantages:

• Complex server and client implementations.
• May not be suitable for all use cases due to its complexity.

Use Cases: WebSockets are well-suited for real-time applications like online gaming, collaborative editing, and instant messaging.

When to use which polling method:

• Use Regular Polling when you can tolerate some delay in data updates, and minimizing server load is not a primary concern.
• Use Long Polling when low latency is important, and you want to reduce the number of requests to the server, but you can handle the complexity of server-side implementation.
• Use Server-Sent Events (SSE) when you need real-time updates in a unidirectional manner and have clients that support SSE.
• Use WebSockets when you need full-duplex, bi-directional, real-time communication between clients and the server. However, consider the added complexity of implementation.

Where not to use polling:

• Avoid polling when real-time updates are absolutely critical, and even a small delay is unacceptable. In such cases, consider using WebSockets or other real-time communication mechanisms.
• Don’t use polling for resources that cannot handle the constant load it generates, as it may lead to performance issues on the server.