Preferred method to store PHP arrays (json_encode vs serialize)

Depends on your priorities.

If performance is your absolute driving characteristic, then by all means use the fastest one. Just make sure you have a full understanding of the differences before you make a choice

• Unlike serialize() you need to add extra parameter to keep UTF-8 characters untouched: json_encode($array, JSON_UNESCAPED_UNICODE) (otherwise it converts UTF-8 characters to Unicode escape sequences).
• JSON will have no memory of what the object's original class was (they are always restored as instances of stdClass).
• You can't leverage __sleep() and __wakeup() with JSON
• By default, only public properties are serialized with JSON. (in PHP>=5.4 you can implement JsonSerializable to change this behavior).
• JSON is more portable

And there's probably a few other differences I can't think of at the moment.

A simple speed test to compare the two

<?phpini_set('display_errors', 1);error_reporting(E_ALL);// Make a big, honkin test array// You may need to adjust this depth to avoid memory limit errors$testArray = fillArray(0, 5);// Time json encoding$start = microtime(true);json_encode($testArray);$jsonTime = microtime(true) - $start;echo "JSON encoded in $jsonTime seconds\n";// Time serialization$start = microtime(true);serialize($testArray);$serializeTime = microtime(true) - $start;echo "PHP serialized in $serializeTime seconds\n";// Compare themif ($jsonTime < $serializeTime) {    printf("json_encode() was roughly %01.2f%% faster than serialize()\n", ($serializeTime / $jsonTime - 1) * 100);}else if ($serializeTime < $jsonTime ) {    printf("serialize() was roughly %01.2f%% faster than json_encode()\n", ($jsonTime / $serializeTime - 1) * 100);} else {    echo "Impossible!\n";}function fillArray( $depth, $max ) {    static $seed;    if (is_null($seed)) {        $seed = array('a', 2, 'c', 4, 'e', 6, 'g', 8, 'i', 10);    }    if ($depth < $max) {        $node = array();        foreach ($seed as $key) {            $node[$key] = fillArray($depth + 1, $max);        }        return $node;    }    return 'empty';}

JSON is simpler and faster than PHP's serialization format and should be used unless:

• You're storing deeply nested arrays:json_decode(): "This function will return false if the JSON encoded data is deeper than 127 elements."
• You're storing objects that need to be unserialized as the correct class
• You're interacting with old PHP versions that don't support json_decode

I've written a blogpost about this subject: "Cache a large array: JSON, serialize or var_export?". In this post it is shown that serialize is the best choice for small to large sized arrays. For very large arrays (> 70MB) JSON is the better choice.