Sampler Performance Analysis Categories

Sampler helps categorize lag into three main types to streamline troubleshooting.

1. Low Memory Issues

Caused when the JVM's heap space is insufficient or a mod has a memory leak.

• Symptoms: Freezes right before the F3 memory counter drops; high CPU load on all cores during freezes; "GC Overhead Limit Exceeded" crashes
• Diagnosis: Check /sampler memory. If the last two rows (GC time) are consistently high after the first few minutes of uptime, the heap size (-Xmx) likely needs to be increased

2. Client-Side Issues

Problems affecting the rendering thread.

• Symptoms: Low FPS; stuttering when moving the mouse; freezes during chunk updates
• Diagnosis: Observe the F3 graph. If the green area is excessively high or jagged, the issue is related to rendering settings, shaders, or complex block models

3. Server-Side Issues

Problems affecting the simulation thread (TPS lag).

• Symptoms: Blocks reappearing after being broken; delayed GUI opening; "Can't keep up" console warnings
• Diagnosis: Use /sampler tps. If the average tick time is significantly above 50ms, use the profiling commands to find the specific entity or tile entity causing the delay