Hello everyone, this is DingCodingCo!!
To mark the end of the year, I’ve prepared a small gift ♥️
As AI writes code on your behalf, backend interviews are increasingly asking, "Why did you choose that approach, and how did you verify it?" rather than "Have you implemented it?"
So, to help you practice answering these questions with numbers you measured yourself, I added four hands-on projects connected to Weeks 3–6 as supplementary material to the textbook.
All of them started from real-world problem scenarios published on the Kakao Pay tech blog, and I wrote the textbook based on the results of implementing and running them myself.
Additional Appendices
1. [Week 3] Is removing Filesort from a statistical query with an index really enough?
→ The index that eliminated Filesort was not the fastest index.
2. [Week 4] Did turning off just one OSIV setting bring the connection pool back to life?
→ Under the same load, the failure rate dropped from 39% → 0%. The key was where the external API call was made, not the setting.
3. [Week 5] How should we send UPDATEs in a points accrual batch?
→ By leaving JPA as is and changing only the settings, processing 100,000 records went from 54 seconds → 6.4 seconds.
4. [Week 6] Would moving the GROUP BY in a statistical batch to Redis make it faster?
→ Redis won when "already calculated values were not calculated again."
Each appendix follows the order of “problem → run it yourself → transfer it to your résumé,” and also includes PAAR examples that you can add directly to your résumé, along with follow-up interview questions.
You can open it after completing the corresponding week.
Please refer to the textbook for details!
I hope you have an end of the year filled with all sorts of experimentation ♥️♥️♥️