XGROUP DELCONSUMER

Introduction and Use Case(s)

XGROUP DELCONSUMER is a Redis command used in the context of stream processing. It allows you to remove a specific consumer from a consumer group without deleting the group itself. This can be particularly useful in scenarios where consumers are dynamically added and removed, or if a consumer has completed its task and should no longer participate in processing messages.

Syntax

  1. XGROUP DELCONSUMER <stream> <groupname> <consumername>

Parameter Explanations

  • <stream>: The name of the stream from which the consumer group is associated.
  • <groupname>: The name of the consumer group you want to modify.
  • <consumername>: The name of the consumer to be removed from the group.

Return Values

The command returns an integer indicating the number of pending messages owned by the deleted consumer. If the consumer does not exist, it returns 0.

Code Examples

  1. dragonfly> XADD mystream * name Alice age 30
  2. "1654329474169-0"
  3. dragonfly> XADD mystream * name Bob age 25
  4. "1654329485521-0"
  5. dragonfly> XGROUP CREATE mystream mygroup $ MKSTREAM
  6. OK
  7. dragonfly> XREADGROUP GROUP mygroup Alice COUNT 1 STREAMS mystream >
  8. 1) 1) "mystream"
  9.    2) 1) "1654329474169-0"
  10.       2) 1) "name"
  11.          2) "Alice"
  12.          3) "age"
  13.          4) "30"
  14. dragonfly> XREADGROUP GROUP mygroup Bob COUNT 1 STREAMS mystream >
  15. 1) 1) "mystream"
  16.    2) 1) "1654329485521-0"
  17.       2) 1) "name"
  18.          2) "Bob"
  19.          3) "age"
  20.          4) "25"
  21. dragonfly> XGROUP DELCONSUMER mystream mygroup Alice
  22. (integer) 1
  23. dragonfly> XINFO CONSUMERS mystream mygroup
  24. 1) 1) "name"
  25.    2) "Bob"
  26.    3) "pending"
  27.    4) (integer) 1
  28.    5) "idle"
  29.    6) (integer) 0

Best Practices

  • Ensure that the consumer you intend to delete has indeed finished processing all its pending messages, or handle reassigning those messages before deletion.
  • Regularly monitor the state of your streams and consumer groups using commands like XINFO to maintain optimal performance and resource usage.

Common Mistakes

  • Trying to delete a consumer that does not exist, which will simply return 0.
  • Not properly handling pending messages from the consumer being deleted, potentially leading to unprocessed data.

FAQs

What happens to the pending messages of the deleted consumer?

The pending messages need to be handled separately as they do not automatically get reassigned. You may use commands like XPENDING to review and manage these messages.

Can I delete a consumer group using XGROUP DELCONSUMER?

No, XGROUP DELCONSUMER is only for removing individual consumers. To delete a consumer group, use XGROUP DESTROY.