SLOWLOG

Introduction and Use Case(s)

The SLOWLOG command in Redis is used to help diagnose performance issues by logging commands that exceed a specified execution time. This tool is useful for identifying slow-running queries, debugging, and optimizing performance.

Syntax

  1. SLOWLOG subcommand [argument]

Parameter Explanations

  • subcommand: The specific operation to be performed on the slow log. Common subcommands include:
    • GET [count]: Retrieves the slow log entries, optionally limiting the number of entries returned.
    • LEN: Returns the length of the slow log.
    • RESET: Clears all entries from the slow log.

Return Values

  • SLOWLOG GET [count]: An array of slow log entries, each entry consisting of an entry ID, timestamp, execution time (in microseconds), and the executed command.
  • SLOWLOG LEN: An integer indicating the number of entries in the slow log.
  • SLOWLOG RESET: A simple string reply indicating success, usually “OK”.

Code Examples

  1. dragonfly> SLOWLOG GET 2
  2. 1) 1) (integer) 10
  3.    2) (integer) 1625077765
  4.    3) (integer) 1500
  5.    4) 1) "SET"
  6.       2) "key"
  7.       3) "value"
  8. 2) 1) (integer) 8
  9.    2) (integer) 1625077705
  10.    3) (integer) 2000
  11.    4) 1) "HSET"
  12.       2) "hash"
  13.       3) "field"
  14.       4) "value"
  16. dragonfly> SLOWLOG LEN
  17. (integer) 5
  19. dragonfly> SLOWLOG RESET
  20. "OK"

Best Practices

  • Regularly monitor the slow log to catch performance issues early.
  • Adjust the slowlog-log-slower-than configuration parameter to an appropriate threshold based on your application’s performance requirements.

Common Mistakes

  • Failing to clear the slow log (SLOWLOG RESET) can result in an excessively large log if not monitored regularly.
  • Misinterpreting the execution time; it is measured in microseconds, not milliseconds.

FAQs

How do I configure what constitutes a “slow” query?

You can set the slowlog-log-slower-than configuration parameter in your redis.conf file or at runtime using the CONFIG SET command.

What is the default length of the slow log?

The default length of the slow log is 128 entries. You can adjust this using the slowlog-max-len configuration parameter.