A Junior Developer's Open Source Contribution Story

KakaoPay's Money Clan team introduced Kafka and MongoDB for a new project. In particular, they chose MongoDB, which supports non-blocking I/O, to match the characteristic that all requests are processed using the Fire-and-Forget pattern.

However, after completing the MongoDB connection pool configuration, they discovered a problem where the application continuously generated INFO logs stating that a new connection had been established every minute. This led to a log pollution issue that unnecessarily increased the size of the log files.

To trace the '1-minute' cycle that didn't exist in any configuration value, they began analyzing the internal implementation of the mongodb-driver-core module. They went through the process of examining the driver's core code, including ConnectionPoolSettings.java, to identify the root cause of the problem.