Monitoring and websites performance links

20 Linux System Monitoring Tools Every SysAdmin Should Know
top, vmstats, w, uptime, ps, everything you need to know to monitor linux server performance

SQL Injection Attack
Presentation of SQL injection attacks, and how to prevent them in your code

Asynchronous/parallel HTTP requests using PHP multi_curl
How to work with web services with asynchronous/parallel requests using curl and curl_multi*

Even Faster Web Sites
How to optimize the loading of js, css, resources in your page, using cache and various HTML options

mk query digest
Perl profiler for memcached