Compare redis queries performance similar to SQL selects. Learnt hard by example on production code problems

1. Piotr Wasiak, PRUG 10.2023
In memory, key-value store

2. NoSQL
• called also Non Relational
• NoSQL systems are also sometimes called "Not only SQL"
• SQL syntax is not supported

3. Redis
What for?
• Cache
• Storing noSQL data (structures)
• Background jobs data in queues

4. Why Redis is one of the top noSQL db?
• Fast
• Proven technology
• Well community among many programming languages
• Data structures in values

5. Kredis and data structures

6. Kredis and data structures

7. Background jobs
Sidekiq
* https://www.holistics.io/blog/how-we-built-a-multi-tenant-job-queue-system-with-postgresql-ruby/

8. Persistance?
What happen when we restart Redis server?
• by default there is no data anymore
• you can have non structured dump to
fi
le to restore on crash/restart

9. Screw-up
Custom Redis usage
• We have events in system
• We have to send webhooks on:
• event start
• event end

10. Screw-up
Custom Redis usage
• On event add (and in failover job)
• Set enqueued job_ids in Redis with keys:
• "ac_noti
fi
cations.start.1244"
• "ac_noti
fi
cations.end.1244"
• On event postpone, get from redis job_ids, delete them from sidekiq queue
and repeat above procedure after create callback
• After Redis restart we have also a job to ensure that future events
will be re-enqueued if no entries in Redis

11. Custom Key Search on Redis
• Redis.keys
•

12. https://dev.to/molly/how-to-safely-navigate-redis-with-ruby-j9l

13. Custom Key Search on Redis
• Redis.keys
• Redis.scan_each(match: "ac_noti
fi
cations.??*.1244")
•

14. SQL tables
https://www.tutorialgateway.org/sql-create-table/

15. Redis tests
Redis in separate docker component

16. Redis tests
Redis in separate docker component

17. Redis tests
Redis in separate docker component

18. Custom Key Search on Redis
• Redis.keys
• Redis.scan_each(match: "ac_noti
fi
cations.??*.1244")
• Multiple gets
• Redis.get 'ac_noti
fi
cations.start.1244' => job_id_10
• Redis.get 'ac_noti
fi
cations.end.1244' => job_id_10

20. Rails creator DHH about Redis

22. Why to use DB for caching?
From DHH keynote
• Disk space is 10x more cheaper than RAM (using Redis)
• Cache life time can be months
(we can have persistent Redis also, but not such big as DB)
• Sharding (not trivial for Redis)
• 1 less process if you already use disk DB
• Is multithreaded in comparison to Redis :D
• Why not ?
• it's slower 0,5 times than Redis

23. Sources
• Rails World opening DHH Ketnote
• https://dev.to/molly/how-to-safely-navigate-redis-with-ruby-j9l
• Transactions in Redis (Go example)