Jeff blogs, "DTrace is a dynamic tracing facility for performance analysis and troubleshooting that lets system administrators and developers examine running systems, including system calls and kernel actions. DTrace enables you to explore your system to understand how it works, track down performance problems, or locate the cause of errors. DTrace lets you create custom programs or quick "one liners" to dynamically instrument the system and provide immediate answers to arbitrary questions you can formulate using the DTrace D programming language.
DTrace is intended for production systems, and can be used to troubleshoot performance problems and errors by gathering and aggregating information about system behavior..."
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