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XGROUP CREATECONSUMER

Introduction​

In Dragonfly, as well as in Redis and Valkey, the XGROUP CREATECONSUMER command is used to explicitly create a consumer within a consumer group for a stream. This command is part of the streams data type which facilitates managing consumer groups and processing data in a distributed manner.

Syntax​

XGROUP CREATECONSUMER key group consumer

Parameter Explanations​

  • key: The key of the stream for which the consumer is being created.
  • group: The name of the consumer group within the stream.
  • consumer: The name of the consumer to be added to the specified group.

Return Values​

  • The command returns 1 if a new consumer is successfully created.
  • If the consumer already exists, it returns 0.

Code Examples​

Basic Example​

Create a new consumer in a consumer group:

# Create a stream with items
dragonfly$> XADD mystream * field1 value1
"1609471230723-0"

dragonfly$> XGROUP CREATE mystream mygroup 0
OK

# Create a consumer named 'consumer-1' in 'mygroup'.
dragonfly$> XGROUP CREATECONSUMER mystream mygroup consumer-1
(integer) 1

Attempt to Create an Existing Consumer​

Recreate the same consumer to demonstrate the return value:

# Attempt to create an existing consumer.
dragonfly$> XGROUP CREATECONSUMER mystream mygroup consumer-1
(integer) 0 # Consumer already exists.

Best Practices​

  • Ensure unique consumer names within a group to prevent operational conflicts.
  • Utilize consumer groups for efficient distributed data processing and to maintain a balanced load among consumers.

Common Mistakes​

  • Not creating the consumer group before adding consumers, which will result in an error.
  • Using the wrong key or group, leading to failed consumer creation attempts.

FAQs​

What happens if the consumer group does not exist?​

If the specified consumer group does not exist, XGROUP CREATECONSUMER will return an error. Ensure the group is created with XGROUP CREATE before adding consumers.

Can a consumer belong to multiple groups?​

Consumers are specific to the consumer group they are created within. A consumer with the same name can exist in different groups, handling messages independently in each context.