Production Baseline JVM Flags Start every Java 17 production deployment with this baseline: java \ # GC — choose one (see GC section) -XX:+UseG1GC \ -XX:MaxGCPauseMillis=200 \ \ # Heap sizing -Xms4g -Xmx4g \ \ # GC logging — essential for diagnosis -Xlog:gc*:file=/var/log/app/gc.log:time,uptime,level,tags:filecount=5,filesize=20m \ \ # OOM diagnostics -XX:+HeapDumpOnOutOfMemoryError \ -XX:HeapDumpPath=/var/log/app/heap-dump.hprof \ -XX:+ExitOnOutOfMemoryError \ \ # Metaspace -XX:MaxMetaspaceSize=512m \ \ # Code cache -XX:ReservedCodeCacheSize=512m \ \ # JFR — always-on profiling -XX:StartFlightRecording=duration=0,filename=/var/log/app/profile.

The Production Mindset Migrating to Java 21 unlocks new capabilities, but production readiness requires deliberate configuration. The JVM defaults are conservative — designed to work reasonably across a wide range of workloads, not to be optimal for any specific one. This article covers: Which JVM flags to set for every production Java 21 deployment GC selection and tuning for different workload profiles Virtual thread configuration and monitoring Container-aware JVM settings Observability and profiling Startup and memory optimization JVM Flags: The Production Baseline Start every Java 21 production deployment with this baseline flag set: