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XSETID

Introduction​

In Dragonfly, as well as in Redis and Valkey, the XSETID command is used to set the ID of an existing consumer group in a stream. This command allows you to manually manage the last delivered ID of a consumer group, which can be particularly useful in scenarios where you need precise control over message processing.

Syntax​

XSETID key groupname id

Parameter Explanations​

  • key: The key of the stream for which you want to set the consumer group ID.
  • groupname: The name of the consumer group whose last delivered ID you want to set.
  • id: The new ID you want to assign as the last delivered ID of the consumer group. This should be a valid stream ID.

Return Values​

The command returns OK if the ID for the consumer group is successfully set.

Code Examples​

Basic Example​

Set the last delivered ID for a consumer group:

dragonfly> XGROUP CREATE mystream mygroup 0
OK
# Assuming some entries have been added to the stream...
dragonfly> XSETID mystream mygroup 1526569495631-0
OK

Changing the Last Delivered ID​

Imagine you have read up to a certain message ID, and you want to mark this as the new last delivered ID:

# Add some entries to the stream
dragonfly> XADD mystream * message "Hello World"
1526569495631-0
dragonfly> XADD mystream * message "Another Message"
1526569495632-0

# Now change the last delivered ID for `mygroup`
dragonfly> XSETID mystream mygroup 1526569495632-0
OK

This ensures that the consumer group acknowledges up to the specified message ID.

Error Handling​

Attempt to set a last delivered ID that doesn't exist:

dragonfly> XSETID mystream mygroup 9999999999999-0
(error) ERR The specified ID is greater than the maximal ID in the stream

Best Practices​

  • Ensure the provided id exists in the stream; otherwise, the command will return an error.
  • Use XSETID carefully, as setting the wrong ID can lead to message delivery inconsistencies.

Common Mistakes​

  • Setting an ID that does not exist in the stream.
  • Overwriting the last delivered ID in a way that skips some messages unintentionally.

FAQs​

What happens if the consumer group does not exist?​

If the consumer group does not exist, XSETID will return an error because there is no group to set the ID for.

Can I use wildcard or relative IDs?​

No, you must specify an exact stream ID that exists in the stream.