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XINFO CONSUMERS

Introduction​

In Dragonfly, as well as in Redis and Valke, the XINFO CONSUMERS command is used to retrieve information about the consumers of a consumer group for a given stream. This command is helpful for monitoring the activity of consumers connected to a specific stream and can assist in troubleshooting and performance tuning.

Syntax​

XINFO CONSUMERS key group
  • Time complexity: O(1)
  • ACL categories: @read, @stream, @slow

Parameter Explanations​

  • key: The key of the stream.
  • group: The name of the consumer group whose consumers' information you want to retrieve.

Return Values​

  • The command returns an array of information about each consumer in the consumer group.
  • Each element in the array is a dictionary with details such as the consumer name, idle time, pending message count, etc.

Code Examples​

Retrieve Information of Consumers​

Get information about consumers in a consumer group:

dragonfly$> XGROUP CREATE mystream mygroup $ MKSTREAM
OK

dragonfly$> XADD mystream * field1 value1
"1736319841099-0"

dragonfly$> XADD mystream * field2 value2
"1736319844825-0"

# Read from the stream using consumer-1.
dragonfly$> XREADGROUP GROUP mygroup consumer-1 COUNT 1 STREAMS mystream >
1) 1) "mystream"
   2) 1) 1) "1736319841099-0"
         2) 1) "field1"
            2) "value1"

# Get information about consumers in the consumer group.
# The output shows the consumer name, pending message count, and idle time.
dragonfly$> XINFO CONSUMERS mystream mygroup
1) 1) "name"
   2) "consumer-1"
   3) "pending"
   4) (integer) 1
   5) "idle"
   6) (integer) 5000 # Idle time in milliseconds.

# Read from the stream using consumer-2.
dragonfly$> XREADGROUP GROUP mygroup consumer-2 COUNT 1 STREAMS mystream >
1) 1) "mystream"
   2) 1) 1) "1736319844825-0"
         2) 1) "field2"
            2) "value2"

# Get information about consumers in the consumer group.
# Now there are two consumers in the group, and the output shows details for both.
dragonfly$> XINFO CONSUMERS mystream mygroup
1) 1) "name"
   2) "consumer-1"
   3) "pending"
   4) (integer) 1
   5) "idle"
   6) (integer) 50000 # Idle time in milliseconds.
2) 1) "name"
   2) "consumer-2"
   3) "pending"
   4) (integer) 1
   5) "idle"
   6) (integer) 5000 # Idle time in milliseconds.

Best Practices​

  • Regularly monitor consumer metrics to ensure that your consumer groups are efficiently processing messages.
  • Use consumer idle time to detect inactive consumers and potentially rebalance workloads.

Common Mistakes​

  • Failing to create a consumer group before using XINFO CONSUMERS will result in an error.
  • Misunderstanding the interpretation of idle time; it might lead to incorrect assumptions about consumer activity.

FAQs​

What happens if the stream or consumer group does not exist?​

If the stream or consumer group does not exist, the XINFO CONSUMERS command will return an error indicating that the specified key or group does not exist.

Can I use XINFO CONSUMERS for streams without consumer groups?​

No, the XINFO CONSUMERS command is specifically for use with streams that have consumer group(s) defined.