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nrk / predis


Flexible and feature-complete Redis client for PHP and HHVM



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Predis is a flexible and feature-complete Redis client library for PHP >= 5.3.

By default this library does not require any additional C extension, but it can be optionally paired with phpiredis to lower the overhead of serializing and parsing the Redis RESP Protocol. An asynchronous implementation of Predis is available through Predis\Async (experimental).

Predis can be used with HHVM >= 2.3.0 but there are no guarantees you will not run into unexpected issues (especially when the JIT compiler is enabled via Eval.Jit = true) due to HHVM being still under heavy development and not yet 100% compatible with the standard PHP.

More details about this project can be found on the frequently asked questions and on the wiki.

Main features

  • Support for a wide range of Redis versions (from 2.0 to 3.0) using profiles.
  • Clustering via client-side sharding using consistent hashing or custom distributors.
  • Smart support for redis-cluster (Redis >= 3.0).
  • Support for master-slave replication (write operations on master, read operations on slaves).
  • Transparent key prefixing for all known Redis commands using a customizable prefixing strategy.
  • Command pipelining (works on both single nodes and aggregate connections).
  • Abstraction for Redis transactions (Redis >= 2.0) supporting CAS operations (Redis >= 2.2).
  • Abstraction for Lua scripting (Redis >= 2.6) with automatic switching between EVALSHA or EVAL.
  • Abstraction for SCAN, SSCAN, ZSCAN and HSCAN (Redis >= 2.8) based on PHP iterators.
  • Connections to Redis are established lazily by the client upon the first command.
  • Support for both TCP/IP and UNIX domain sockets and persistent connections.
  • Support for Webdis (requires both ext-curl and ext-phpiredis).
  • Support for custom connection classes for providing different network or protocol backends.
  • Flexible system for defining custom commands and server profiles.

How to use Predis

Predis is available on Packagist which allows a quick installation using Composer. Alternatively, the library can be found on our own PEAR channel for a more traditional installation via PEAR. Ultimately, archives of each release are available on GitHub.

Loading the library

Predis relies on the autoloading features of PHP to load its files when needed and complies with the PSR-4 standard. Autoloading is handled automatically when dependencies are managed through Composer, but it is also possible to leverage its own autoloader in projects or scripts not having any autoload facility:

// Prepend a base path if Predis is not available in your "include_path".
require 'Predis/Autoloader.php';


It is possible to create a phar archive directly from the repository by launching bin/create-phar. The phar contains a stub defining its own autoloader so you just need to require() it to start using the library. Ultimately it is possible to generate a single big PHP file containing all the source code simply by launching bin/create-single-file, but this practice is not encouraged.

Connecting to Redis

When creating a client instance without passing any connection parameter, Predis assumes and 6379 as default host and port. The default timeout for the connect() operation is 5 seconds:

$client = new Predis\Client();
$client->set('foo', 'bar');
$value = $client->get('foo');

Connection parameters can be supplied either in the form of URI strings or named arrays. The latter is the preferred way to supply parameters, but URI strings can be useful when parameters are read from non-structured or partially-structured sources:

// Parameters passed using a named array:
$client = new Predis\Client([
    'scheme' => 'tcp',
    'host'   => '',
    'port'   => 6379,

// Same set of parameters, passed using an URI string:
$client = new Predis\Client('tcp://');

Starting with Predis v1.0.2 the client also understands the redis scheme in URI strings as defined by the provisional IANA registration.

The actual list of supported connection parameters can vary depending on each connection backend so it is recommended to refer to their specific documentation or implementation for details.

When an array of connection parameters is provided, Predis automatically works in cluster mode using client-side sharding. Both named arrays and URI strings can be mixed when providing configurations for each node:

$client = new Predis\Client([
    ['host' => '', 'alias' => 'second-node'],

See the aggregate connections section of this document for more details.

Client configuration

Various aspects of the client can be configured simply by passing options to the second argument of Predis\Client::__construct():

$client = new Predis\Client($parameters, ['profile' => '2.8', 'prefix' => 'sample:']);

Options are managed through a mini DI-alike container while their values can be lazily initialized only when needed. This is a list of the options supported by default:

  • profile: which profile to use in order to match a specific version of Redis.
  • prefix: a prefix string that is automatically applied to keys found in commands.
  • exceptions: whether the client should throw or return responses upon Redis errors.
  • connections: connection backends or a connection factory to be used by the client.
  • cluster: which backend to use for clustering (predis, redis or custom configuration).
  • replication: which backend to use for replication (predis or custom configuration).
  • aggregate: custom connections aggregator (overrides both cluster and replication).

Users can provide custom options with their values or lazy callable initializers that are stored in the options container for later use through the library.

Aggregate connections

Predis is able to aggregate multiple connections which is the base for clustering and replication. By default the client implements a cluster of nodes using either client-side sharding (default) or a Redis-backed solution using redis-cluster. As for replication, Predis can handle a single-master and multiple-slaves setup by executing read operations on slaves and switching to the master only for write operations. The replication behavior is fully configurable.


The client can be configured to operate in a master-slave setup by executing read-only commands on slave nodes and automatically switch to the master node as soon as it detects a command that will perform a write operation. This is the basic configuration needed to work with replication:

// Parameters require one master node specifically marked with `alias=master`.
$parameters = ['tcp://', 'tcp://'];
$options    = ['replication' => true];

$client = new Predis\Client($parameters, $options);

While Predis is able to distinguish commands performing write and read-only operations, EVAL and EVALSHA represent a corner case in which the client switches to the master node because it cannot tell when a Lua script is safe to be executed on slaves. While this is indeed the default behavior, when certain Lua scripts do not perform write operations it is possible to provide an hint to tell the client to stick with slaves for their execution:

$parameters = ['tcp://', 'tcp://'];
$options    = ['replication' => function () {
    // Set scripts that won't trigger a switch from a slave to the master node.
    $strategy = new Predis\Replication\ReplicationStrategy();

    return new Predis\Connection\Aggregate\MasterSlaveReplication($strategy);

$client = new Predis\Client($parameters, $options);
$client->eval($LUA_SCRIPT, 0);             // Sticks to slave using `eval`...
$client->evalsha(sha1($LUA_SCRIPT), 0);    // ... and `evalsha`, too.

The examples directory contains two complete scripts showing how replication can be configured for basic and complex scenarios.


Simply passing an array of connection parameters to the client constructor configures Predis to work in cluster mode using client-side sharding. If you, on the other hand, want to leverage Redis >= 3.0 nodes coordinated by redis-cluster, then the client must be initialized like this:

$parameters = ['tcp://', 'tcp://'];
$options    = ['cluster' => 'redis'];

$client = new Predis\Client($parameters, $options);

When using redis-cluster it is not necessary to pass all of the nodes that compose your cluster, you can specify only a few nodes and the client will automatically fetch the full and updated slots map directly from Redis by contacting one of the servers.

NOTE: our support for redis-cluster does not currently consider master / slave replication but this feature will be added in a future release of the library.

Command pipelines

Pipelining can help with performances when many commands need to be sent to a server by reducing the latency introduced by network round-trip timings. Pipelining also works with aggregate connections. The client can execute the pipeline inside a callable block or return a pipeline instance with the ability to chain commands thanks to its fluent interface:

// Executes a pipeline inside the given callable block:
$responses = $client->pipeline(function ($pipe) {
    for ($i = 0; $i < 1000; $i++) {
        $pipe->set("key:$i", str_pad($i, 4, '0', 0));

// Returns a pipeline that can be chained thanks to its fluent interface:
$responses = $client->pipeline()->set('foo', 'bar')->get('foo')->execute();


The client provides an abstraction for Redis transactions based on MULTI and EXEC with a similar interface to command pipelines:

// Executes a transaction inside the given callable block:
$responses = $client->transaction(function ($tx) {
    $tx->set('foo', 'bar');

// Returns a transaction that can be chained thanks to its fluent interface:
$responses = $client->transaction()->set('foo', 'bar')->get('foo')->execute();

This abstraction can perform check-and-set operations thanks to WATCH and UNWATCH and provides automatic retries of transactions aborted by Redis when WATCHed keys are touched. For an example of a transaction using CAS you can see the following example.

Adding new commands

While we try to update Predis to stay up to date with all the commands available in Redis, you might prefer to stick with an old version of the library or provide a different way to filter arguments or parse responses for specific commands. To achieve that, Predis provides the ability to implement new command classes to define or override commands in the default server profiles used by the client:

// Define a new command by extending Predis\Command\Command:
class BrandNewRedisCommand extends Predis\Command\Command
    public function getId()
        return 'NEWCMD';

// Inject your command in the current profile:
$client = new Predis\Client();
$client->getProfile()->defineCommand('newcmd', 'BrandNewRedisCommand');

$response = $client->newcmd();

There is also a method to send raw commands without filtering their arguments or parsing responses. Users must provide the list of arguments for the command as an array, following the signatures as defined by the Redis documentation for commands:

$response = $client->executeRaw(['SET', 'foo', 'bar']);

Script commands

While it is possible to leverage Lua scripting on Redis 2.6+ using EVAL and EVALSHA directly, Predis offers script commands as an higher level abstraction built upon them to make things simple. Script commands can be registered in the server profile used by the client and are accessible as if they were plain Redis commands, but they define Lua scripts that get transmitted to the server for remote execution. Internally they use EVALSHA by default and identify a script by its SHA1 hash to save bandwidth, but EVAL is used as a fall back when needed:

// Define a new script command by extending Predis\Command\ScriptCommand:
class ListPushRandomValue extends Predis\Command\ScriptCommand
    public function getKeysCount()
        return 1;

    public function getScript()
        return <<<LUA
local rnd = tostring(math.random())'lpush', KEYS[1], rnd)
return rnd

// Inject the script command in the current profile:
$client = new Predis\Client();
$client->getProfile()->defineCommand('lpushrand', 'ListPushRandomValue');

$response = $client->lpushrand('random_values', $seed = mt_rand());

Customizable connection backends

Predis can use different connection backends to connect to Redis. Two of them leverage a third party extension such as phpiredis resulting in major performance gains especially when dealing with big multibulk responses. While one is based on PHP streams, the other is based on socket resources provided by ext-socket. Both support TCP/IP and UNIX domain sockets:

$client = new Predis\Client('tcp://', [
    'connections' => [
        'tcp'  => 'Predis\Connection\PhpiredisStreamConnection',  // PHP stream resources
        'unix' => 'Predis\Connection\PhpiredisSocketConnection',  // ext-socket resources

Developers can create their own connection classes to support whole new network backends, extend existing classes or provide completely different implementations. Connection classes must implement Predis\Connection\NodeConnectionInterface or extend Predis\Connection\AbstractConnection:

class MyConnectionClass implements Predis\Connection\NodeConnectionInterface
    // Implementation goes here...

// Use MyConnectionClass to handle connections for the `tcp` scheme:
$client = new Predis\Client('tcp://', [
    'connections' => ['tcp' => 'MyConnectionClass'],

For a more in-depth insight on how to create new connection backends you can refer to the actual implementation of the standard connection classes available in the Predis\Connection namespace.


Reporting bugs and contributing code

Contributions to Predis are highly appreciated either in the form of pull requests for new features, bug fixes, or just bug reports. We only ask you to adhere to a basic set of rules before submitting your changes or filing bugs on the issue tracker to make it easier for everyone to stay consistent while working on the project.

Test suite

ATTENTION: Do not ever run the test suite shipped with Predis against instances of Redis running in production environments or containing data you are interested in!

Predis has a comprehensive test suite covering every aspect of the library. This test suite performs integration tests against a running instance of Redis (>= 2.4.0 is required) to verify the correct behavior of the implementation of each command and automatically skips commands not defined in the specified Redis profile. If you do not have Redis up and running, integration tests can be disabled. By default the test suite is configured to execute integration tests using the profile for Redis 2.8 (which is the current stable version of Redis) but can optionally target a Redis instance built from the unstable branch by modifying phpunit.xml and setting REDIS_SERVER_VERSION to dev so that the development server profile will be used. You can refer to the tests README for more detailed information about testing Predis.

Predis uses Travis CI for continuous integration and the history for past and current builds can be found on its project page.


Project related links



The code for Predis is distributed under the terms of the MIT license (see LICENSE).