C10K problem

The C10K Problem

What is it?

The C10K Problem (“10,000 Connections”) refers to the challenge of building a server capable of handling 10,000 concurrent client connections efficiently on a single machine.

Coined by :contentReference[oaicite:0]{index=0} in 1999.

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Why was it a Problem?

Traditional servers used:

1 Thread / Process per Connection

10,000 clients
= 10,000 threads
= huge memory + context switching overhead

This approach does not scale well.

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Solution

Use:

• Non-blocking I/O
• Event loops
• I/O multiplexing (select, poll, epoll, kqueue)
• Async programming

1 Thread
   ↓
Event Loop
   ↓
10,000+ Connections

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Technologies Inspired by C10K

• :contentReference[oaicite:1]{index=1}
• :contentReference[oaicite:2]{index=2}
• Java NIO
• Go goroutines
• Netty
• libuv

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Interview Takeaway

The C10K problem demonstrated that thread-per-request architectures do not scale to massive concurrency. Modern systems solve this using non-blocking I/O, event loops, and asynchronous processing, allowing a small number of threads to handle thousands of simultaneous connections efficiently.