Help Center/ Distributed Cache Service/ FAQs/ Redis Usage/ Dispersing Keys in a Cluster Instance
Updated on 2025-04-10 GMT+08:00
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Dispersing Keys in a Cluster Instance

A Redis cluster distributes data across multiple nodes by hashing keys into 16,384 slots. Each key is mapped to a specific hash slot using a hash function.

However, keys with similar patterns may be mapped to the same hash slot, leading to uneven distribution across the cluster. To avoid this, do as follows to disperse keys.

Dispersing Keys in a Cluster Instance

  1. By hash tags

    Hash tags can effectively disperse keys but the keys' logic must be consistent.

    Redis controls key distribution using hash tags. A hash tag is contained in a brace pair {} and a hash value is calculated only by it.

    Example:

    Keys:

    user:1 user:2 user:3

    These keys may be hashed to one slot. To prevent this, use hash tags:

    user:{1} user:{2} user:{3}

    Redis calculates hash values based on {1}, {2}, and {3}, and distributes keys to different slots.

  2. By random key names

    Random key names effectively balance loads but may increase key complexity.

    When hash tags are not available, add random strings or UUIDs to key names to disperse keys.

    Example:

    import uuid

def generate_key(base_key):
    random_part = str(uuid.uuid4())[:8]  # Randomly generates an 8-bit string.
    return f"{base_key}:{random_part}"

# Use
key = generate_key("user")
print(key)  # user:123e4567

    Keys can be dispersed based on a random part contained in each key.

  3. By varying key prefixes

    If key naming is fixed, add different prefixes to disperse keys.

    Example:

    user:1 -> user1:1 
user:2 -> user2:2 
user:3 -> user3:3

    Different key prefixes result in distinct hash values.

Querying Slot Distribution

Use the CLUSTER INFO and CLUSTER KEYSLOT commands.

Example:

redis-cli -c -h <node_ip> -p <node_port> CLUSTER INFO 
redis-cli -c -h <node_ip> -p <node_port> CLUSTER KEYSLOT <key>
Parent topic: Redis Usage