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XLEN

Introduction​

In Dragonfly, as well as in Redis and Valkey, the XLEN command is used to determine the number of entries in a stream. The command is useful for monitoring and managing data streams, providing quick insights into the size and health of your data pipeline.

Syntax​

XLEN key

Parameter Explanations​

  • key: The key of the stream for which you wish to know the number of entries.

Return Values​

  • The command returns the number of entries in the specified stream as an integer.

Code Examples​

Basic Example​

Determine the number of entries in a stream:

dragonfly$> XADD mystream * sensor-1-temperature 23.1
"1678819562090-0"

dragonfly$> XADD mystream * sensor-2-temperature 23.2
"1678819562091-0"

dragonfly$> XADD mystream * sensor-3-temperature 23.3
"1678819562092-0"

dragonfly$> XLEN mystream
(integer) 3

Non-Existent Stream​

Check the length of a non-existent stream:

dragonfly$> XLEN non-existent-stream
(integer) 0

Best Practices​

  • Regularly check stream lengths as part of a comprehensive data management strategy.
  • Integrate XLEN into your monitoring dashboards to provide real-time feedback on stream sizes and help detect bottlenecks or unusual activity patterns.

Common Mistakes​

  • Using XLEN on non-stream data types will result in an error, so ensure that the key provided is indeed a stream.
  • Confusing XLEN with list length commands like LLEN, as they apply to different data structures.

FAQs​

What happens if the stream key does not exist?​

If the stream key does not exist, XLEN returns 0.

Can XLEN be used to determine entries in other data types like lists or sets?​

No, XLEN is specifically designed for streams. To determine the length of other data types, use the appropriate commands such as LLEN for lists or SCARD for sets.