GC logs are essential for resolving memory and CPU issues, and enhancing application performance. With the release of Java 9 in September 2017, a Unified GC logging framework was introduced alongside new logging system properties. Java 9 removed 43 old GC flags, necessitating replacements. Tools like GCeasy offer analysis of the revamped log format.
Enabling GC logging enhances application performance by reducing response time, aiding in memory issue troubleshooting, forecasting outages, and improving capacity planning without significant overhead. For Java 8 and below, specific JVM arguments enable logging, and for Java 9 and above, alternative commands are used. Analyzing GC logs requires tools like GCeasy due to varied formats.
GC logs detail the time taken for GC events, reporting 'user', 'sys', and 'real' times. 'Real' time is the elapsed clock time, while 'user' and 'sys' times reflect CPU time in user-mode and kernel, respectively. Real time can exceed user + sys time due to heavy I/O activity or lack of CPU, indicating potential performance issues.