Tell me about your real-world experience with GC optimization — were there pauses lasting tens of seconds, and how did you optimize them?

In one of the projects, we encountered an issue with long garbage collection (GC) pauses, reaching up to tens of seconds, which significantly affected the system's responsiveness.

To optimize, I took the following steps:

1. Memory analysis and profiling. Using tools (e.g., VisualVM, JProfiler), I identified that the main load was on the Old Generation, with frequent full garbage collections.

2. JVM parameter tuning. I increased the heap size to reduce the frequency of collections, and configured GC parameters (e.g., switched to G1 GC with pause time optimization).

3. Code optimization. I analyzed sections creating many temporary objects and reduced their number to lessen GC load.

4. Load separation. In some cases, I moved heavy operations to separate services or processes to reduce the load on the main application.

Example JVM configuration for G1 GC with pause time limit:

java -XX:+UseG1GC -XX:MaxGCPauseMillis=200 -Xmx4g -Xms4g -jar app.jar

As a result, I managed to reduce pauses to a few hundred milliseconds, significantly improving the stability and performance of the application.