Java Profilers - Yash-777/MyWorld GitHub Wiki

A Java profiler is a tool used to monitor, analyze, and optimize the performance of Java applications. It helps developers identify bottlenecks, memory leaks, high CPU usage, and other runtime issues by providing insights into CPU usage, heap memory, garbage collection, thread activity, and more.

Profilers are essential in both development and production environments for ensuring application performance, stability, and efficient resource usage.

Purpose

• The main purposes of Java profilers include:
• Analyzing CPU and memory usage
• Detecting memory leaks and inefficient object allocations
• Monitoring thread behavior and synchronization issues
• Understanding garbage collection (GC) behavior
• Improving overall application performance

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Popular Open-Source Java Profilers

• Description: A graphical tool for monitoring and profiling Java applications.
• Features: CPU and memory profiling, heap dump analysis, thread monitoring, and GC stats.
• Integration: Bundled with older JDKs (up to JDK 8); extendable via plugins.

VisualVM^github is a visual tool integrating commandline JDK tools and lightweight profiling capabilities.
Designed for both development and production time use.

• Getting Started
• Troubleshooting Guide
• Getting Started Extending VisualVM

VisualVM that says?	The limit of 64k instrumented methods has been reached
Means that the Java agent used for profiling or instrumentation (often the Sampler or Profiler in VisualVM) has hit the maximum number of methods (64,000 or 64k) that it can instrument during a single run. This is a limitation of the underlying Java instrumentation engine, particularly when doing bytecode instrumentation for profiling purposes.

🛠 VisualVM: 64k Instrumented Methods Limit – Workarounds

If you see the error: "The limit of 64k instrumented methods has been reached"

This occurs due to VisualVM’s profiler hitting its method instrumentation cap.

✅ Workarounds:

• Use Sampling Instead of Profiling
  • Go to Profiler → CPU and select Sampler (instead of Instrumented).
  • Avoids the 64k method limit; suitable for most performance analyses.
• Limit Instrumentation Scope
  • Navigate to Tools → Options → Profiler → Instrumentation.
  • Include only your application packages (e.g., com.myapp.*).
  • Exclude frameworks/libraries (e.g., java.*, org.springframework.*).
• Use Alternative Profilers
  • For large apps needing full instrumentation: try YourKit, JProfiler, or Async Profiler(used under the hood by some modern tools like IntelliJ’s profiler or perf on Linux).

ℹ️ Note: The 64k limit is internal to the Java profiler engine; it cannot be increased.