What best practices should be followed when reviewing and optimizing PHP code for performance, especially in older scripts that may not have been optimized in the past?

When reviewing and optimizing PHP code for performance, especially in older scripts, it is important to focus on identifying bottlenecks, reducing unnecessary database queries, optimizing loops and conditionals, and utilizing caching mechanisms. Additionally, consider refactoring code to make it more efficient and reducing the use of global variables. 

// Example code snippet demonstrating optimization techniques

// Avoid unnecessary database queries by fetching data only once and storing it in variables
$query = "SELECT * FROM users";
$result = mysqli_query($connection, $query);
$users = mysqli_fetch_all($result, MYSQLI_ASSOC);

// Optimize loops by minimizing the number of iterations and avoiding nested loops if possible
foreach ($users as $user) {
    // Process user data
}

// Utilize caching mechanisms like memcached or Redis to store frequently accessed data and reduce database queries
$cacheKey = 'users_data';
if (!($usersData = getFromCache($cacheKey))) {
    $usersData = fetchDataFromDatabase();
    setToCache($cacheKey, $usersData);
}

// Refactor code to make it more efficient and reduce the use of global variables
function processUserData($user) {
    // Process user data without relying on global variables
}

Keywords

code review performance optimization legacy code PHP functions error handling

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