How many socket connections possible?

I achieved 1600k concurrent idle socket connections, and at the same time 57k req/s on a Linux desktop (16G RAM, I7 2600 CPU). It's a single thread http server written in C with epoll. Source code is on github, a blog here.

Edit:

I did 600k concurrent HTTP connections (client & server) on both the same computer, with JAVA/Clojure . detail info post, HN discussion: http://news.ycombinator.com/item?id=5127251

The cost of a connection(with epoll):

• application need some RAM per connection
• TCP buffer 2 * 4k ~ 10k, or more
• epoll need some memory for a file descriptor, from epoll(7)

Each registered file descriptor costs roughly 90 bytes on a 32-bit kernel, and roughly 160 bytes on a 64-bit kernel.

This depends not only on the operating system in question, but also on configuration, potentially real-time configuration.

For Linux:

cat /proc/sys/fs/file-max

will show the current maximum number of file descriptors total allowed to be opened simultaneously. Check out http://www.cs.uwaterloo.ca/~brecht/servers/openfiles.html

10,000? 70,000? is that all :)

FreeBSD is probably the server you want, Here's a little blog post about tuning it to handle 100,000 connections, its has had some interesting features like zero-copy sockets for some time now, along with kqueue to act as a completion port mechanism.

Solaris can handle 100,000 connections back in the last century!. They say linux would be better

The best description I've come across is this presentation/paper on writing a scalable webserver. He's not afraid to say it like it is :)

Same for software: the cretins on the application layer forced great innovations on the OS layer. Because Lotus Notes keeps one TCP connection per client open, IBM contributed major optimizations for the ”one process, 100.000 open connections” case to Linux

And the O(1) scheduler was originally created to score well on some irrelevant Java benchmark. The bottom line is that this bloat benefits all of us.