TCP

http://articles.techrepublic.com.com/5100-10878_11-1050878.html -- "TCP/IP options for high-performance data transmission"
http://www.ussg.iu.edu/hypermail/linux/kernel/0102.0/0943.html -- LKML thread, "TCP_NOPUSH on FreeBSD, TCP_CORK on Linux"
http://www.irbs.net/internet/postfix/0707/1097.html -- postfix thread, "dkim-milter signing terribly slow with Postfix, but not with sendmail"
- This becomes: "TCP_NODELAY, TCP_CORK, TCP_NOPUSH, etc (was: dkim-milter signing terribly slow...)"

Portable APIs

TCP_NODELAY: Disable Nagle's algorithm (coalescing of small packets until an ACK is received or a retransmission triggered). See the Linux APIs page for interactions with TCP_CORK on that platform.