Profiling & Benchmarking (JVisualVM, YourKit) - Q&A

Profiling is the process of monitoring and analyzing the runtime performance of a Java application to identify bottlenecks, memory leaks, and inefficient code execution.

JVisualVM is a Java performance monitoring and troubleshooting tool that provides insight into CPU usage, memory consumption, and thread activity in real-time.

YourKit is a commercial Java profiler that offers more advanced features such as deeper memory analysis, CPU sampling, and integration with IDEs compared to JVisualVM.

JVisualVM can be started by running the jvisualvm command from the command line if the Java Development Kit (JDK) is installed.

Benchmarking measures the performance of code execution in terms of CPU usage, execution time, and memory allocation to compare optimizations.

JVisualVM provides heap dumps, garbage collection analysis, and memory sampler tools that help detect memory leaks by analyzing object retention.

The two main types of profiling are CPU profiling (measuring method execution time) and memory profiling (analyzing object allocations and memory usage).

Remote monitoring can be enabled by starting the Java application with the -Dcom.sun.management.jmxremote options and configuring JMX connections.

Sampling profiling captures method execution times at intervals with low overhead, while instrumentation modifies bytecode to track every method call for detailed analysis.

YourKit provides call tree analysis, hot spots detection, and flame graphs to visualize CPU bottlenecks in a Java application.

A heap dump is a snapshot of the Java heap memory at a specific point in time, useful for analyzing memory usage, detecting leaks, and identifying large objects.

In JVisualVM, you can take a heap dump by selecting the target application, navigating to the "Monitor" tab, and clicking "Heap Dump."

A thread dump captures the state of all running threads, useful for debugging deadlocks, while a heap dump provides memory allocation details.

YourKit detects memory leaks by analyzing retained objects, identifying unreachable yet uncollected objects, and tracking heap usage trends.

A GC log records details about garbage collection events, helping in optimizing memory management and diagnosing performance issues.

GC logging can be enabled using JVM options such as -XX:+PrintGCDetails and -Xlog:gc in Java 9+.

CPU sampling is a low-overhead profiling technique that periodically records stack traces to estimate method execution time.

YourKit and JProfiler are both commercial Java profilers, but YourKit is known for its low overhead and deep memory analysis, while JProfiler provides more advanced integration with IDEs.

Object allocation tracking monitors the creation of objects in memory, helping identify excessive allocations that may impact performance.

JVisualVM allows measuring method execution time using the "Profiler" tab by enabling CPU profiling and analyzing method call times.

The "Monitor" tab in JVisualVM provides real-time insights into CPU usage, heap memory, thread activity, and garbage collection statistics.

JVisualVM's "Threads" tab shows thread states, blocked threads, and deadlocks, helping diagnose thread contention issues.

A hot spot is a method or section of code that consumes a significant amount of CPU time, making it a key target for optimization.

YourKit provides a "Hot Spots" view that lists methods consuming the most CPU time, allowing developers to focus on optimizing them.

Live memory analysis tracks object allocations in real time, helping developers identify excessive memory usage and potential leaks.

JVisualVM allows periodic heap dumps and memory sampling, which can be compared to track memory growth and detect leaks.

A retained set is a group of objects that would be removed from memory if a particular object were garbage collected, helping in leak detection.

YourKit identifies memory leaks by analyzing object retention graphs, detecting unreferenced objects, and tracking heap growth trends.

Shallow size is the memory consumed by an object itself, while retained size includes the memory of all objects retained exclusively by that object.

Arguments like -XX:+UnlockDiagnosticVMOptions and -XX:+DebugNonSafepoints can improve profiling accuracy by providing better stack trace sampling.