Predis Alias Sharding - php

Question

I'm trying to use Predis sharding by alias, as described here. My code is basically identical, but I'm only returning empty arrays. Do my hash keys need {} around them? (EDIT: Nope, just tried it)
$api->get("/test", function () {
$servers = [
["alias" => "metadata", "port" => 6380],
["alias" => "relations", "port" => 6381],
["alias" => "dim_provider", "port" => 6382],
["alias" => "dim_revctrcode", "port" => 6383],
["alias" => "dim_enccode", "port" => 6384],
["alias" => "dim_pos", "port" => 6385]
];
$options = [
"nodehash" => function ($connection) { return $connection->getParameters()->alias; },
"cluster" => function ($options) {
$replicas = Predis\Cluster\Distribution\HashRing::DEFAULT_REPLICAS;
$hashring = new Predis\Cluster\Distribution\HashRing($replicas, $options->nodehash);
$cluster = new Predis\Connection\PredisCluster($hashring);
return $cluster;
}
];
$redis = new Predis\Client($servers, $options);
try {
$test = $redis->scard("dim_provider");
print_r($test); // Prints 0 for scard or empty Array for hgetall
} catch (Exception $e) {
print $e->getMessage();
}
$redis = new Predis\Client(["port" => 6382]);
$test = $redis->scard("dim_provider");
print_r($test); // Works.
});
EDIT: It also works if I only put one server in the $servers array. So it seems the hashing is not working right. When I throw some echos in front of the return value in nodehash I can see that it's returning the alias.

Answer 1

Assigning a dim_provider alias to a Redis connection and trying to get a key named dim_provider from a server are two different things.
In your script you are trying to set up a cluster of Redis instances using connection aliases (instead of the usual ip:port pairs) to calculate the distribution of your keyspace among multiple Redis servers acting as your data shards. Using this setup, the key dim_provider is sharded accordingly to the underlying distribution algorithm and could be stored on any of the 6 servers composing your cluster and defined in the $servers array.

Answer 2

I wanted to add how trivially easy it was to implement my clustering strategy once nrk got me on the right track. This is a really well-written library.
$api->get("/test", function () {
Class KeyCluster extends Predis\Connection\PredisCluster {
public function __construct() {
$this->pool = Array();
}
public function add (Predis\Connection\SingleConnectionInterface $connection) {
$parameters = $connection->getParameters();
if (isset($parameters->table)) {
$this->pool[$parameters->table] = $connection;
} else {
$this->pool[] = $connection;
}
}
public function getConnection (Command\CommandInterface $command) {
$key = $command->getArgument(0);
$table = explode(":", $key)[0];
return isset($this->pool[$table]) ? $this->pool[$table] : null;
}
}
$redis = new Predis\Client([
"tcp://127.0.0.1:6382?table=dim_provider",
"tcp://127.0.0.1:6383?table=dim_pos"
],[
"cluster" => new KeyCluster
]);
$result = $redis->scard("dim_provider");
print_r($result);
});