Profiling and Tuning Tools and Techniques

Google-perftools
Google's open source performance profiling tool. Works on Linux and C++ for now.

Detect Memory Leaks
Tools and tips on detecting Java and C++ memory leaks in your app, especially under heavy workload

Detect Hung Threads
Find which Java class is causing the hang.

Socket Performance
Change a small thing in your network code and increase its throughput big!

Find Slow Queries
Scripts that can let you set event monitors and capture output in text for analysis.

Linux CPU Profiler
Find which piece of code is consuming the most CPU cycles.