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The C10k problem refers to the problem of optimising socket server software to handle a large number of clients at the same time (hence the name C10k - concurrent ten thousand connections). The problem of socket server optimisation has been studied because a number of factors must be considered to allow a web server to support many clients. This can involve a combination of operating system constraints and web server software limitations.
While there are some specialized web servers that can handle more than ten thousand client connections, most web servers currently handle at most ten thousand clients simultaneously.
The problem's name is a numeronym for "ten thousand clients".
Servers which address the problem 
Several web servers have been developed to counter the C10K problem:
- nginx, which relies on an event-driven (asynchronous) architecture, instead of threads, to handle requests (WordPress.com uses nginx to solve the C10K problem)
- Lighttpd, which relies on an asynchronous architecture to handle requests
- Cherokee, a lightweight web server
- Tornado, a non-blocking web server and web application framework written in Python (used by Facebook's FriendFeed)
- Apache AWF (retired, formerly Apache Deft), asynchronous, non-blocking web server running on the JVM
- JBoss Netty, a NIO client server framework which enables quick and easy development of network applications such as protocol servers and clients
- EventMachine, an asynchronous, non-blocking web server running on Ruby EventMachine
- Yaws, a web server written in Erlang; profiting from Erlang's extremely lightweight processes.
- Cowboy, an other, very lightweight, web server written in Erlang
- asyncore (in the standard Python library), a non-blocking web server library. It is based on Medusa, which is no longer maintained.
- IIS, Microsoft's flagship web server, through the use of asynchronous requests, as demonstrated by third-party components such as WebSync
- Jetty asynchronous Java servlet container
- pyftpdlib, an extremely fast and scalable FTP server written in Python
- Xitrum, an async and clustered Scala web framework and HTTP(S) server based on Netty
- Django, some research is being done using the asynchronous IO support in Python 3.3.
- Vibe.d, a simple asynchronous I/O web framework written in D
There is a benchmark done for comparing the performance of various web frameworks supporting c10k solutions.
See also 
External links