http://dyn.com/open-dialogue/dynamic-discourse/dns/educational/how-we-got-dyndns-com-to-load-faster-and-how-you-can-learn-from-it the subj. how to optimize webpage load speed by compressing, optimizing images, js, css
http://www.westnet.com/~gsmith/content/postgresql/chkp-bgw-83.htm improvements to PostgreSQL that could be made by tuning wal/background writer processes
http://fasterdata.es.net/TCP-tuning/ Excellent site provides both theoretical background and practical recommendation for the situation when you need to push limits of TCP links using regular OS and commodity hardware. Especially useful if you need to do it via long-haul fast TCP link, i.e. the situation when you normally use specialized networking hardware (read: cisco)
http://www.google.com/url?sa=t&source=web&ct=res&cd=2&url=http%3A%2F%2Fwww.academypublisher.com%2Fjnw%2Fvol02%2Fno03%2Fjnw02030617.pdf&ei=-4zzSZ38FpywtAP0sLDPCg&rct=j&q=Linux+sofware+router%3A+data+plane+optimizations&usg=AFQjCNE5OzutnNt9SWgOaMcZydC5jLXTwg in-depth linux routing performance evaluation, including code profiling, execution path analysis, etc
http://www.google.com/firefox?client=firefox-a&rls=org.mozilla:en-US:official about optimization, speed, scaling web apps. Useful not only to php programmers, but to web app developers in general
http://revsys.com/writings/postgresql-performance.html yet another postgresql tuning guide, contains useful explanation of most omportant config parameters
http://momjian.us/main/writings/pgsql/hw_performance/index.html notes on PostgreSQL tuning from Bruce Momjian (PostgreSQL core team )
http://www.ibm.com/developerworks/linux/library/l-scalability/?ca=dgr-lnxw02FasterLinuxNet SMP and network performace in linux (tcp only, no forwarding)
http://www.softwareprojects.com/resources/programming/t-i-can-make-your-site-run-10-times-faster-1462.html nice summary for the above
http://www.devside.net/articles/apache-performance-tuning “Premature optimization is the root of all evil.” – Donald Knuth.