Lab: JVM Memory Analysis

Goal

Analyze JVM memory usage and configure garbage collection settings for optimal performance.

Learning Objectives

• Understand JVM memory regions (Heap, Stack, Metaspace)
• Enable and interpret GC logs
• Compare different garbage collectors
• Use JVM tuning flags

Pre-requisites

• Java 17+ installed
• Basic understanding of Java memory model

Tasks

Task 1: Create Memory-Intensive Application

Create a Java application that allocates memory progressively.

Starter Code Provided: MemoryLabApp.java

Task 2: Run with GC Logging

Run the application with the following JVM flags:

java -Xms128m -Xmx256m -Xlog:gc*:file=gc.log:time,uptime MemoryLabApp

Questions to Answer:

1. How many Minor GCs occurred? - 6
2. How many Major/Full GCs occurred? - 7
3. What was the longest GC pause time? - 9.343ms

Task 3: Compare Garbage Collectors

Run the application with different GC algorithms:

# Serial GC
java -XX:+UseSerialGC -Xmx256m -Xlog:gc*:file=gc-serial.log MemoryLabApp

# G1GC
java -XX:+UseG1GC -Xmx256m -Xlog:gc*:file=gc-g1.log MemoryLabApp

# ZGC (Java 11+)
java -XX:+UseZGC -Xmx256m -Xlog:gc*:file=gc-zgc.log MemoryLabApp

Record your observations in a table:

GC Type	Total GC Events	Longest Pause	Throughput
Serial	6	25.018	99.9%
G1GC	22	18.124	99.92%
ZGC	28	5.557	99.9%

Task 4: Tune for Low Latency

Configure G1GC to target a maximum pause time of 100ms:

java -XX:+UseG1GC -XX:MaxGCPauseMillis=100 -Xmx256m MemoryLabApp

Questions:

1. Did G1GC achieve the target pause time? yes
2. What trade-offs did you observe? It seemed to be more inconsistent

Deliverables

1. Completed MemoryLabApp.java
2. GC log files from each run
3. Answers to all questions in a markdown file

Starter Code

See starter_code/MemoryLabApp.java