Concept
- HTTP Short Connection (Non-persistent Connection): A TCP connection is established for each HTTP request-response, and it is immediately closed after completion.
- HTTP Long Connection (Persistent Connection): Multiple HTTP requests and responses can be sent continuously over the same TCP connection, which remains open for a period of time, allowing the reuse of that connection for multiple requests.
Summary of Differences
Advantages and Disadvantages
Short Connection
Advantages:
- Simple implementation, easy to manage, and resources are easily released.
- Avoids resource waste caused by long-term connection occupation.
Disadvantages:
- Each request requires 3-way handshake and 4-way teardown, resulting in high network overhead and latency.
- Suitable for low-frequency, single-request scenarios, not suitable for high-frequency or large numbers of requests.
Long Connection
Advantages:
- Multiple requests can reuse the same TCP connection, significantly reducing the overhead and latency of establishing/closing connections.
- Increases system throughput, suitable for high-concurrency access.
- Avoids the consumption of ports and kernel resources caused by frequent TCP connection establishment.
Disadvantages:
- Long-term connection occupation requires reasonable timeout settings; otherwise, it wastes server resources and may be exploited for DoS attacks.
- The server needs a mechanism to manage and recycle idle connections.
Typical Application Scenarios
Short Connection
- Email, simple form submissions, one-time API calls, and other low-interaction frequency products.
- Services with few TCP connections, low pressure, and no need for connection reuse.
Long Connection
- High-frequency communication between web front-end and back-end (e.g., single-page applications, API services).
- Instant messaging (IM), online chat, real-time push notifications.
- Businesses requiring multiple, frequent requests (e.g., image carousel loading, message push servers).
Supplement
- HTTP/1.0 defaults to short connections, which can be made long connections using
<span>Connection: keep-alive</span>; - HTTP/1.1 defaults to long connections unless explicitly stated with
<span>Connection: close</span>; - New protocols like WebSocket/HTTP2 are more efficient and stateful than HTTP long connections, but their principles are similar to long connections.
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