PUBSUB SHARDCHANNELS

Introduction and Use Case(s)

The PUBSUB SHARDCHANNELS command in Redis is used to list active shard channels. Shard channels are a type of Pub/Sub channel that allows for more granular control over message distribution, typically used in scenarios requiring selective message broadcasting based on predefined shards.

Syntax

  1. PUBSUB SHARDCHANNELS [pattern]

Parameter Explanations

  • pattern: (Optional) A glob-style pattern to filter the shard channels. If provided, only the channels matching this pattern will be listed. If omitted, all active shard channels will be returned.

Return Values

The command returns an array of strings where each string is the name of an active shard channel.

Example Outputs

  1. When no pattern is provided:

    1. 1) "shard:channel:1"
    2. 2) "shard:channel:2"

  2. When a pattern is provided:

    1. 1) "shard:channel:1"

Code Examples

  1. dragonfly> PUBSUB SHARDCHANNELS
  2. 1) "shard:channel:1"
  3. 2) "shard:channel:2"
  5. dragonfly> PUBSUB SHARDCHANNELS shard:channel:*
  6. 1) "shard:channel:1"
  7. 2) "shard:channel:2"
  9. dragonfly> PUBSUB SHARDCHANNELS shard:channel:1
  10. 1) "shard:channel:1"

Best Practices

  • Use specific patterns to avoid listing an overwhelming number of channels when working in large-scale applications.
  • Regularly monitor active shard channels to ensure efficient resource utilization.

Common Mistakes

  • Not using patterns when necessary, leading to performance issues by trying to list too many channels at once.
  • Assuming the command filters on exact matches rather than supporting glob-style patterns.

FAQs

What is a shard channel in Redis?

A shard channel allows messages to be distributed to subsets of subscribers based on predefined shards, facilitating more granular message control compared to regular Pub/Sub channels.

Can I use multiple patterns with PUBSUB SHARDCHANNELS?

No, the command accepts only one pattern at a time to filter the shard channels.

How does PUBSUB SHARDCHANNELS differ from PUBSUB CHANNELS?

PUBSUB SHARDCHANNELS lists only active shard channels, while PUBSUB CHANNELS lists all active channels, including non-shard ones.