Troubleshooting
Real-world problem-solving experiences from production environments.
Changed MySQL Column Type from bigint to varchar and It Got 8x Slower...! : Procedure Performance Degradation Troubleshooting
Introduction Hello. I’m Jeongil Jeong, a 3rd-year backend developer working at a proptech platform. Today, I’d like to share an interesting performance issue that occurred in our service and the resolution process. While solving a problem where a MySQL procedure suddenly became 8 times slower, I enc...
October 20, 2025
Resolving DB Replication Lag
I’m sharing about a replication lag issue I encountered at work. Problem Occurrence Our company uses database replication to distribute load and improve performance. The system is configured as Active-Active redundancy in a Master-Slave structure, and through ProxySQL, SELECT statements are sent to ...
November 15, 2024
[Troubleshooting] QueryDSL StackOverflowError Investigation
I’m sharing about a Querydsl StackOverflow issue I encountered at work. Problem Occurrence As always, the problem starts with a Slack message. As soon as I received the message, I couldn’t help but react with “huh?” StackOverflow? Was there recursively implemented code in the server? What is StackOv...
March 15, 2024
[Troubleshooting] Failed Graceful Shutdown During Kubernetes Pod Scale In, Journey to Find Lost Async Logic
I’m sharing about a failed Graceful Shutdown issue I encountered at work. Problem Occurrence Usually, I encounter exceptions and problem situations through Slack quite often. Today, I encountered a problem differently than usual. This problem started with a back office user’s inquiry. “I think one p...
February 9, 2024
[Troubleshooting] Journey to Resolving HikariCP Deadlock When Using JPA and MyBatis Together (feat. OSIV)
I’m sharing an issue related to HikariCP Deadlock that I encountered at work. Problem Occurrence As always, the issue starts with a Slack message. Excerpt from Stack trace Caused by: org.apache.ibatis.exceptions.PersistenceException: ###Error querying database. Cause: org.springframework.jdbc.Cannot...
January 9, 2024
Spring Batch Job Concurrent Registration Deadlock Issue (Deadlock accessing creating a job on sqlserver when multiple jobs start at once)
I’d like to share a Spring Batch-related issue I encountered at work. Problem Occurrence The issue started with an error message in Slack. It was a stack trace indicating that a Deadlock had occurred on our company’s Batch server. Naturally, since Deadlock could severely impact the service, I immedi...
November 20, 2023