Predis for PHP: Complete Guide with Examples

What is Predis and why is it needed

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Predis is a full-featured client for working with Redis (Remote Dictionary Server) in PHP. Redis is a high-performance key-value data store, often used for caching, session management, message queues, and real-time applications. Predis allows PHP applications to interact with a Redis server by sending commands and receiving responses.

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Why use Predis? Unlike other clients (e.g., phpredis), Predis is written entirely in PHP and does not require installing additional C extensions. This makes it an ideal choice for environments where you cannot control extension installation (e.g., shared hosting). Predis supports all major Redis features: strings, hashes, lists, sets, transactions, Pub/Sub, clustering, and much more.

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Main use cases:

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• Caching — speeding up your website by storing frequently requested data in memory.
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• Session management — storing user sessions in Redis for fast access and scalability.
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• Task queues — organizing background task processing using Redis lists.
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• Ratings and counters — using sorted sets to build leaderboards.
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• Pub/Sub — implementing real-time messaging systems.
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Installing Predis

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Predis is distributed via Composer, the standard package manager for PHP. Make sure you have Composer installed. If not, download it from getcomposer.org.

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To install Predis, run the following command in the root of your project:

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composer require predis/predis

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After installation, a vendor folder and a composer.json file will appear in your project. To include Predis, use the Composer autoloader:

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require 'vendor/autoload.php';

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Minimum requirements: PHP 7.2 or higher. Predis does not require the Redis PHP extension, as it implements the Redis protocol in pure PHP.

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Quick start with code example

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Let's write a simple script that connects to Redis, saves a value, and reads it.

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<?php\nrequire 'vendor/autoload.php';\n\nuse Predis\\Client;\n\n// Create a Redis client (default connects to localhost:6379)\n$client = new Client();\n\n// Set a value\n$client->set('greeting', 'Hello, Redis!');\n\n// Get the value\n$value = $client->get('greeting');\necho $value; // Outputs: Hello, Redis!\n\n// Check if the key exists\nif ($client->exists('greeting')) {\n    echo "Key exists!";\n}\n\n// Delete the key\n$client->del(['greeting']);\n?>

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This code does the following:

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1. Connects to the Redis server on localhost (port 6379).
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2. Saves the string "Hello, Redis!" under the key "greeting".
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3. Reads the value back and prints it.
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4. Checks if the key exists.
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5. Deletes the key.
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If Redis is running on a different host or port, pass connection parameters:

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$client = new Client([\n    'scheme' => 'tcp',\n    'host'   => '192.168.1.100',\n    'port'   => 6379,\n]);

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Main Predis methods

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Predis provides a convenient interface for all Redis commands. Let's look at the 10 most commonly used methods with detailed examples.

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1. set — setting a value

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What it does: Sets the value for the specified key. If the key already exists, its value is overwritten.

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Parameters:

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• $key (string) — the key name.
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