How to increase value of tcbhashsize parameter in OS X
sysctl is the tool of choice for this. sysctl net.inet.tcp.tcbhashsize will tell you its value, and sysctl -w net.inet.tcp.tcbhashsize=new_value will set the value. However on my system I got the error sysctl: oid 'net.inet.tcp.tcbhashsize' is read only when I tried to set the value – no idea if it's possible to set this value in some way without compiling and running your own kernel.