What are the potential pitfalls of relying on a database entry to determine online status for registered users?

Potential pitfalls of relying on a database entry to determine online status for registered users include: - Database queries can be slow and resource-intensive, leading to delays in updating online status. - Users may not always log out properly, causing their online status to remain active even when they are not. - Network issues or server downtime can prevent real-time updates to online status. To address these issues, a more efficient solution would be to use a combination of database entries and session variables to track user online status. By updating the database only when a user logs in or out, and using session variables to quickly check online status during a user's session, we can reduce the strain on the database and ensure more accurate real-time updates.

// Update online status in database when user logs in or out
function updateOnlineStatus($userId, $status) {
    // Update online status in database for user with $userId
    // $status should be 'online' or 'offline'
}

// Check user's online status using session variable
function isUserOnline($userId) {
    // Check if user with $userId has an active session
    return isset($_SESSION['user_' . $userId]);
}

// Example usage
$userId = 123;
if (isUserOnline($userId)) {
    echo 'User is online';
} else {
    echo 'User is offline';
}