persistent-connections

Why is second API call faster than first?

Per Wikipedia: “Persistent connections keep TCP/TLS open after response so next HTTP exchange skips handshake — called keep-alive.”

Like keeping phone line open — second question does not need redial.

1. First request does TCP+TLS+HTTP
2. Server replies with Connection: keep-alive
3. Socket stays open idle
4. Second request reuses socket
5. Timeout closes after idle

• Saves 1-2 RTT per reuse
• Needs idle timeout
• Head-of-line blocking in HTTP/1.1
• HTTP/2 multiplexes over one

• Built from: HTTP — persistence is HTTP feature
• Related: HTTP Request Response Cycle — cycle benefits
• Related: HTTP Versions — HTTP/1.1 added keep-alive
• Contrasts with: Statelessness — stateless but transport reused

• Leaking sockets — no close on error
• Pooling without limit — too many open