Introduction to Cluster Key Slot

The cluster-key-slot is an essential feature in Redis Cluster, which plays a crucial role in distributing data across different nodes. This article provides an introduction to cluster-key-slot and explains its functionality with several practical API examples. We’ll also build an application to showcase how to effectively use these APIs.

Why Cluster Key Slot?

In a distributed environment, the data needs to be evenly distributed across various nodes. The cluster-key-slot ensures data distribution by hashing keys to consistent slots. This helps in balancing the load and ensures optimal performance.

API Examples

1. Getting the Cluster Key Slot

To obtain the key slot for a specific key, use the CLUSTER KEYSLOT command. This command returns the slot number for the given key.

  
    redis-cli> CLUSTER KEYSLOT user:1000
    (integer) 15355
  

2. Adding Nodes to a Cluster

Adding nodes to an existing cluster can be done using the CLUSTER MEET command. This command takes the IP address and port of the new node.

  
    redis-cli> CLUSTER MEET 192.168.1.100 7000
  

3. Cluster Nodes

The CLUSTER NODES command lists all the nodes in the cluster with their status.

  
    redis-cli> CLUSTER NODES
  

4. Moving Slots

You can move slots between nodes using the CLUSTER SETSLOT command. This allows you to reassign a slot from one node to another.

  
    redis-cli> CLUSTER SETSLOT 15355 NODE <node-id>
  

Application Example

Below is a simple Node.js application that utilizes Redis Cluster and demonstrates the use of cluster-key-slot.

  
    const redis = require('redis');

    const cluster = redis.createCluster({
      rootNodes: [
        {
          url: 'redis://localhost:7000'
        }
      ],
      useReplicas: true
    });

    (async () => {
      await cluster.connect();

      await cluster.set('user:1000', 'John Doe');
      const slot = await cluster.cluster('keyslot', 'user:1000');
      
      console.log(\`Slot for user:1000 is \${slot}\`);

      await cluster.disconnect();
    })();
  

This application connects to a Redis Cluster, sets a key-value pair, retrieves the slot for the given key, and prints it to the console.

By understanding the cluster-key-slot feature and utilizing the related APIs, you can effectively manage data distribution within your Redis Cluster and optimize its performance.

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