How does accessing external data in PHP affect traffic usage for the user?

Accessing external data in PHP can increase traffic usage for the user because each request to an external source requires data to be transferred over the network. To minimize the impact on traffic usage, it is recommended to cache the external data locally and only refresh it periodically or when necessary. 

// Example of caching external data in PHP
$cache_file = 'external_data_cache.json';
$cache_expiry = 3600; // 1 hour

if (file_exists($cache_file) && time() - filemtime($cache_file) < $cache_expiry) {
    $data = file_get_contents($cache_file);
} else {
    $data = file_get_contents('http://example.com/external_data');
    file_put_contents($cache_file, $data);
}

// Process $data as needed

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