How many socket connections possible?

Question

Has anyone an idea how many tcp-socket connections are possible on a modern standard Linux server?

(There is in general less traffic on each connection, but all the connections have to be up all the time.)

Answer 1

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.

Answer 2

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