PHP is a powerful scripting language that is widely used for web development. Every developer should be familiar with essential PHP functions that streamline coding and enhance productivity. Here are 10 essential PHP functions every developer should know:

1. strlen() - This function returns the length of a string, making it essential for validating input.
2. array_merge() - This merges one or more arrays into a single array, which is useful for data manipulation.
3. explode() - This function splits a string by a specified delimiter, allowing you to create arrays from strings easily.
4. implode() - The inverse of explode, implode joins array elements into a string, perfect for output formatting.
5. json_encode() - A crucial function for encoding data into JSON format, essential for APIs and data interchange.

Continuing the list, here are more vital PHP functions you should be aware of:

6. isset() - This function checks if a variable is set and is not null, helping to avoid undefined index notices.
7. empty() - Another popular function, it checks whether a variable is empty, allowing for cleaner condition checks.
8. array_map() - This applies a callback to the elements of the given arrays, which is excellent for functional programming.
9. header() - A powerful function that sends raw HTTP headers, allowing for essential page redirections and content type management.
10. strtotime() - This parses any English textual datetime description into a Unix timestamp, simplifying date manipulations.

Debugging PHP can often feel like searching for a needle in a haystack, but with the right tips and tricks, you can enhance your efficiency and code like a ninja. Begin by utilizing built-in PHP functions such as error_reporting() and ini_set() to manage the error levels you encounter. Additionally, employing var_dump() and print_r() can help you inspect your variables in detail. To streamline your debugging process, consider implementing a debugger like Xdebug, which can provide step-by-step execution and stack traces, making it easier to locate the source of issues.

Another effective strategy is to adopt a consistent debugging routine. This includes isolating code snippets and testing them individually to identify problematic areas. You can create a checklist for common pitfalls, such as:

1. Ensuring variables are defined and initialized correctly
2. Using strpos() to check for string and array occurrences
3. Validating user input to prevent errors

Lastly, don't underestimate the power of code reviews. Collaborating with peers can provide fresh perspectives on your code, making it easier to spot errors and inefficiencies. By incorporating these techniques into your routine, you'll be well on your way to mastering PHP debugging.

Optimizing your PHP code for performance is crucial for enhancing the speed and responsiveness of your web applications. One effective technique is to reduce server requests by minimizing the use of external libraries and frameworks. Additionally, consider implementing caching mechanisms such as OPcache, which can significantly decrease execution times by storing precompiled script bytecode in memory. Furthermore, be mindful of your database queries: always use prepared statements and limit the number of queries in a single transaction to prevent bottlenecks.

Another essential aspect of PHP code optimization is profiling and benchmarking. Utilize tools like Xdebug or Blackfire to identify parts of your code that consume excessive resources. Once you pinpoint these areas, you can refine your logic, eliminate redundancies, and utilize efficient algorithms to improve overall performance. Lastly, do not overlook the importance of using the latest version of PHP, as each release typically includes performance enhancements and new features that can further streamline your application.