JSON or Serialize: What to Choose for Storing PHP Arrays? (Complete Guide)

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Introduction: The Eternal Dilemma of a PHP Developer

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Every PHP developer has at least once faced the task: "How to save an array to a file, database, or cache?" On Stack Overflow, the question "Preferred method to store PHP arrays (json_encode vs serialize)" has gathered thousands of views and dozens of answers. And this is not surprising, because the choice between json_encode() and serialize() affects the performance, compatibility, and even security of your code.

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In this article, we will analyze both methods using real examples, compare their strengths and weaknesses, and give clear recommendations on when to use which. Let's go!

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What is Serialization in PHP?

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Serialization is the process of converting a complex data structure (array, object) into a string that can be saved or transmitted. The reverse process is called deserialization.

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PHP offers two main tools for this task:

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serialize() / unserialize() — PHP's built-in mechanism.
json_encode() / json_decode() — working with the JSON format.

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It would seem that both do the same thing. But the devil, as always, is in the details.

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Example 1: Simple Associative Array

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Let's start with the simplest case — an associative array with user data:

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<?php\n$user = [\n    'name' => 'Alexey',\n    'email' => 'alex@example.com',\n    'age' => 30,\n    'is_admin' => false\n];\n\n// Serialization\n$serialized = serialize($user);\necho $serialized . PHP_EOL;\n// Output: a:4:{s:4:"name";s:14:"Alexey";s:5:"email";s:17:"alex@example.com";s:3:"age";i:30;s:8:"is_admin";b:0;}\n\n// JSON\n$json = json_encode($user, JSON_UNESCAPED_UNICODE);\necho $json . PHP_EOL;\n// Output: {"name":"Alexey","email":"alex@example.com","age":30,"is_admin":false}\n?>

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Even at this stage, the difference is visible: serialize() produces a "dirtier" string with data types (s: — string, i: — integer, b: — boolean). JSON, on the other hand, looks clean and readable.

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Example 2: Multidimensional Array

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Let's complicate the task and save an array with nested data — for example, a list of items in a shopping cart:

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<?php\n$cart = [\n    ['id' => 101, 'name' => 'Book "PHP for Pros"', 'price' => 1500, 'quantity' => 2],\n    ['id' => 102, 'name' => 'Course "JSON Master"', 'price' => 3000, 'quantity' => 1],\n    ['id' => 103, 'name' => 'Certificate', 'price' => 500, 'quantity' => 3]\n];\n\n// Compare string sizes\n$serialized = serialize($cart);\n$json = json_encode($cart, JSON_UNESCAPED_UNICODE);\n\necho "Serialize: " . strlen($serialized) . " bytes\\n";\necho "JSON: " . strlen($json) . " bytes\\n";\n// Output (approximate):\n// Serialize: 218 bytes\n// JSON: 188 bytes\n?>

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Conclusion: JSON is usually more compact, especially for large arrays. This is critical when storing in a database or transmitting over a network.

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Performance: Which is Faster?

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Speed is one of the key factors. Let's test it on 10,000 iterations:

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<?php\n$bigArray = [];\nfor ($i = 0; $i < 1000; $i++) {\n    $bigArray[] = [\n        'id' => $i,\n        'name' => 'Element #' . $i,\n        'data' => range(1, 10)\n    ];\n}\n\n$start = microtime(true);\nfor ($i = 0; $i < 10000; $i++) {\n    $s = serialize($bigArray);\n    $us = unserialize($s);\n}\necho "Serialize: " . (microtime(true) - $start) . " sec\\n";\n\n$start = microtime(true);\nfor ($i = 0; $i < 10000; $i++) {\n    $j = json_encode($bigArray);\n    $uj = json_decode($j, true);\n}\necho "JSON: " . (microtime(true) - $start) . " sec\\n";\n?>

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Results (on PHP 8.2):