XCLAIM

Introduction and Use Case(s)

XCLAIM is a Redis command used in the context of streams to transfer ownership of pending messages from one consumer to another. This is particularly useful in scenarios where the original consumer may have crashed or stalled, and you need to reassign the message for processing by another consumer.

Syntax

  1. XCLAIM <stream> <group> <consumer> <min-idle-time> <ID> [<ID> ...] [IDLE <ms>] [TIME <mstime>] [RETRYCOUNT <count>] [FORCE] [JUSTID]

Parameter Explanations

  • stream: The name of the stream.
  • group: The consumer group that the consumers belong to.
  • consumer: The new consumer that will take ownership of the messages.
  • min-idle-time: Minimum idle time (in milliseconds) that a message must have been idle before it can be claimed.
  • ID: The ID of the message(s) to claim.
  • IDLE <ms>: Optional. Set the idle time (in milliseconds) for the claimed messages.
  • TIME <mstime>: Optional. Sets the last-delivered time in milliseconds epoch format. Useful for copying exact delivery times.
  • RETRYCOUNT <count>: Optional. Updates retry counter for the claimed messages.
  • FORCE: Optional. Claim messages even if they are not idle.
  • JUSTID: Optional. Return only the IDs of the claimed messages, not the message bodies.

Return Values

The XCLAIM command returns the claimed messages. If the JUSTID option is used, it returns only the IDs of the claimed messages.

Examples:

  • Without JUSTID:

    1. dragonfly> XCLAIM mystream mygroup newconsumer 3600000 1526569495631-0
    2. 1) 1) "1526569495631-0"
    3.    2) 1) "field1"
    4.       2) "value1"
    5.       3) "field2"
    6.       4) "value2"

  • With JUSTID:

    1. dragonfly> XCLAIM mystream mygroup newconsumer 3600000 1526569495631-0 JUSTID
    2. 1) "1526569495631-0"

Code Examples

  1. dragonfly> XADD mystream * field1 value1 field2 value2
  2. "1526569495631-0"
  3. dragonfly> XGROUP CREATE mystream mygroup $ MKSTREAM
  4. OK
  5. dragonfly> XREADGROUP GROUP mygroup consumer1 COUNT 1 STREAMS mystream >
  6. 1) 1) "mystream"
  7.    2) 1) 1) "1526569495631-0"
  8.          2) 1) "field1"
  9.             2) "value1"
  10.             3) "field2"
  11.             4) "value2"
  12. dragonfly> XPENDING mystream mygroup
  13. 1) "1526569495631-0"
  14. 2) (integer) 1
  15. 3) (integer) 1626569495631
  16. 4) 1) 1) "consumer1"
  17.       2) (integer) 1
  18. dragonfly> XCLAIM mystream mygroup consumer2 3600000 1526569495631-0
  19. 1) 1) "1526569495631-0"
  20.    2) 1) "field1"
  21.       2) "value1"
  22.       3) "field2"
  23.       4) "value2"

Best Practices

  • Ensure you set an appropriate min-idle-time to avoid claiming messages too early, which might lead to duplicate processing.
  • Use the JUSTID option if you only need the message IDs to optimize performance, especially when dealing with large messages.

Common Mistakes

  • Setting min-idle-time too low, resulting in premature claiming of messages.
  • Forgetting to include the necessary optional parameters (IDLE, TIME, etc.) which might be crucial for specific use cases.
  • Using FORCE without understanding its implications, leading to potential data consistency issues.

FAQs

When should I use the FORCE option?

You should use the FORCE option when you need to claim messages regardless of their idle time. This can be useful in urgent scenarios but use