monline

Using a torrent client with lots of connections my (Snow) Leopard used to get stalled (it just hangs and no app seems to be responding, but the GUI remains mostly functional though). The solution seems to be a bit of a network tweaking.

Create (or edit) the file /etc/sysctl.conf and add the following to it:

Here's a description and the defaults for the above variables ...

• net.inet.tcp.rfc1323 (1): Activate [url=http://en.wikipedia.org/wiki/TCP_window_scale_option
  ]window scaling[/url] and timestamp options according to RFC 1323.
• net.inet.tcp.recvspace (65536): Controls how much buffer space is allocated per socket connection for incoming traffic. This is how much data the kernel will cache on a socket while the application chews on it.
• net.inet.tcp.sendspace (65536): Controls how much buffer space is allocated per socket connection for outgoing traffic. This is how much data the kernel will cache on a socket while the application chews on it.
• net.inet.tcp.win_scale_factor (3): I didn't find much info on this one. Only this: it's advised to increase the value of this variable if you use a gigabit network connection.
• net.inet.tcp.sockthreshold (64): Sets the number of open sockets needed for the system to actually obey your sendspace and recvspace marks.

Further links on the topic:

• https://discussions.apple.com/message/6079960?messageID=6079960
• http://slaptijack.com/system-administration/mac-os-x-tcp-performance-tuning/
• http://gp.darkproductions.com/2008/03/fix-for-slow-wifi-80211-file-transfers.html
• http://thinkwrap.wordpress.com/2007/12/22/fix-for-the-stalled-downloads-in-leopard/
• http://www.psc.edu/networking/projects/tcptune/
• Mac OS X Network Tuning Guide Revisited
• Performance Tuning the Network Stack on Mac OS X 10.6