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XGROUP DELCONSUMER

Introduction​

In Dragonfly, as well as in Redis and Valkey, the XGROUP DELCONSUMER command is used to remove a specific consumer from a consumer group in a stream. This is crucial for managing stream groups by allowing the removal of consumers that are no longer in use. Note that, deleting a consumer makes its pending messages unclaimable. Therefore, be sure to claim or acknowledge any pending messages before removing the consumer from the group.

Syntax​

XGROUP DELCONSUMER key group consumer

Parameter Explanations​

  • key: The key of the stream.
  • group: The name of the consumer group to which the consumer belongs.
  • consumer: The name of the consumer to be removed from the group.

Return Values​

  • An integer representing the number of pending messages that the consumer had before it was deleted.

Code Examples​

Basic Example​

Remove a consumer from a group:

# Create a stream.
dragonfly$> XADD mystream * name "Alice"
"1530105600018-0"

# Create a consumer group.
dragonfly$> XGROUP CREATE mystream mygroup 0
OK

# Add a consumer to the group.
dragonfly$> XREADGROUP GROUP mygroup consumer-1 COUNT 1 STREAMS mystream >
1) 1) "mystream"
   2) 1) 1) "1530105600018-0"
         2) 1) "name"
            2) "Alice"

# Acknowledge the message.
dragonfly$> XACK mystream mygroup "1530105600018-0"
(integer) 1

# Remove the consumer from the group.
# Since the consumer has no pending messages (acknowledged), the return value is 0.
dragonfly$> XGROUP DELCONSUMER mystream mygroup consumer-1
(integer) 0

Best Practices​

  • Regularly monitor and clean up consumers that are no longer active to keep the consumer group healthy.
  • Before removing a consumer, make sure to process and acknowledge all its pending messages, or have another consumer claim its pending messages.

Common Mistakes​

  • Attempting to delete a non-existent consumer, which will result in no effect but can be part of error checks.
  • Removing consumers without acknowledging or reassigning their pending messages, leading to possible message loss.

FAQs​

What happens if the consumer does not exist?​

If the consumer does not exist, the command returns 0, indicating no pending messages were associated with the consumer.

Does this command delete the consumer group itself?​

No, XGROUP DELCONSUMER only removes an individual consumer. The consumer group remains intact until explicitly deleted with the XGROUP DESTROY command.