Direct Answer First Analyzing Java Garbage Collection (GC) logs is essential for diagnosing memory leaks, reducing latency, and optimizing application throughput. GCViewer is a lightweight, open-source desktop tool that visualizes these complex logs into readable charts and actionable data metrics. Prerequisites: Enabling GC Logging
Before you can analyze a log, you must instruct the Java Virtual Machine (JVM) to generate one. The flags you use depend on your Java version.
Java 9 and Newer (Unified JVM Logging):-Xlog:gc*,gc+age=trace,safepoint:file=gc.log:time,uptime,pid:filecount=5,filesize=100M
Java 8 and Older:-XX:+PrintGCDetails -XX:+PrintGCDateStamps -Xloggc:gc.log -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=5 -XX:GCLogFileSize=100M Step 1: Download and Launch GCViewer GCViewer requires a local Java runtime to execute.
Download the latest executable JAR file from the official GitHub repository releases page. Open your terminal or command prompt. Launch the application using the following command: java -jar gcviewer-1.36.jar Use code with caution. (Replace 1.36 with your downloaded version number). Step 2: Load Your GC Log File Once the graphical user interface (GUI) opens: Click File in the top menu bar. Select Open File. Navigate to your generated gc.log file and click Open. Step 3: Read the Visual Chart
GCViewer plots data over time. You can toggle specific lines using the checkboxes on the right panel to de-clutter the view. Blue Line: Current heap size usage. Dirty Orange Line: Total allocated heap size. Red Vertical Lines: Stop-the-World (STW) Full GC pauses.
Black Vertical Lines: Incidental STW pauses (e.g., Young Gen GC). Green Line: Throughput or pause intervals. Step 4: Analyze Key Metrics
Navigate to the Summary and Pause tabs on the bottom half of the screen to view critical health indicators. Throughput
What it means: The percentage of total runtime spent processing application code versus processing garbage collection.
Target: Look for 95% or higher for standard enterprise applications. Pause Times (Latency)
Max Pause: The longest single freeze your application experienced. Avg Pause: The typical duration of a GC pause.
Target: Keep maximum pauses below your application’s network timeout thresholds. Heap Memory Consumption Freed Memory: Total memory reclaimed during cycles.
Accumulation: If the baseline of the blue line (after Full GC) rises continuously over time, your application likely has a memory leak. Common Patterns and Fixes Symptom: Frequent Full GC (Sawtooth Pattern)
Diagnosis: The heap memory is too small, or objects are promoting to the Old Generation too quickly.
Fix: Increase total heap using -Xmx or tune the young generation size with -XX:NewRatio. Symptom: Increasing Baseline Post-Full GC
Diagnosis: Active memory leak. Objects are being held in memory and cannot be collected.
Fix: Take a heap dump (jmap -dump) and analyze it with Eclipse MAT to find the leaking objects. Symptom: Long Initial Pauses Diagnosis: JVM is resizing memory pools on the fly.
Fix: Set the initial heap size (-Xms) equal to the maximum heap size (-Xmx) to prevent dynamic resizing overhead.
To help tailor this guide to your specific performance issues, tell me:
Which Java version and GC algorithm (G1, ZGC, Parallel) are you running?
What symptoms (high CPU, OutOfMemoryError, slow response times) prompted this log analysis? What is the current size of your Java heap? AI responses may include mistakes. Learn more
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