How can one determine the performance bottlenecks in a PHP system and prioritize optimization efforts effectively?

To determine performance bottlenecks in a PHP system, one can use profiling tools like Xdebug or Blackfire.io to analyze the code execution and identify slow-running functions or database queries. Once bottlenecks are identified, prioritize optimization efforts based on the impact on overall performance. This can be done by focusing on optimizing critical sections of code, reducing database queries, optimizing loops, and improving caching mechanisms.

// Example of using Xdebug to profile PHP code
xdebug_start_profiling();

// Code to analyze performance bottlenecks

xdebug_stop_profiling();