Production Tomcat (Java 8) parameter

✔ JVM tuning (temporary mitigation)

-Xms8g
-Xmx8g
-XX:+UseG1GC

⚠️ JVM tuning does not fix leaks, only delays failure.

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🧪 Validation

jcmd <PID> GC.run

Check memory release:

jmap -histo <PID>

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✅ Best Practices (Production / Bank / ISO)

✔ Code review for static leaks
✔ Mandatory resource closing
✔ Regular heap dump analysis
✔ Scheduled Tomcat restart (only if unavoidable)
✔ Monitoring via Prometheus / JMX

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Summary

Area	Action
Root cause	Application code
Detection	Heap dump + GC logs
Fix	Code cleanup
Prevention	Monitoring & best practices

If you want, I can provide:

• Tomcat memory leak SOP

• Heap dump analysis checklist

• Production JVM tuning template

Just let me know.

tomcat memory perameter

Below are the commonly used and recommended Tomcat (JVM) memory parameters, with clear explanations and production-ready examples.

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🔹 Core Tomcat JVM Memory Parameters

1️⃣ Heap Memory

-Xms4g     # Initial heap size
-Xmx4g     # Maximum heap size

Best practice: Keep -Xms = -Xmx for stable performance.

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2️⃣ Metaspace (Java 8+)

-XX:MetaspaceSize=256m
-XX:MaxMetaspaceSize=512m

Controls class metadata memory (important for Tomcat apps).

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3️⃣ Stack Memory (per thread)

-Xss512k

Too many threads + large stack = OutOfMemoryError.

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4️⃣ Garbage Collector (Recommended)

For Java 8+

-XX:+UseG1GC

Optional tuning:

-XX:MaxGCPauseMillis=200
-XX:InitiatingHeapOccupancyPercent=45

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🔹 Memory Leak & Stability Parameters

-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=/opt/tomcat/heapdump
-XX:+ExitOnOutOfMemoryError

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🔹 GC Logging (Java 8)

-XX:+PrintGCDetails
-XX:+PrintGCDateStamps
-Xloggc:/opt/tomcat/logs/gc.log

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🔹 Example: Production Tomcat (Java 8)

Add to setenv.sh:

export CATALINA_OPTS="
-Xms8g
-Xmx8g
-XX:MetaspaceSize=256m
-XX:MaxMetaspaceSize=512m
-Xss512k
-XX:+UseG1GC
-XX:MaxGCPauseMillis=200
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=/opt/tomcat/heapdump
"

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🔹 Check Memory at Runtime

jmap -heap <PID>

jstat -gc <PID> 5s

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✅ Recommended Sizing (Rule of Thumb)

Server RAM	Tomcat Heap
8 GB	4–5 GB
16 GB	8–10 GB
32 GB	16–20 GB

Leave memory for:

• OS

• File cache

• Other services

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⚠️ Common Mistakes

❌ Setting heap larger than system RAM
❌ Ignoring Metaspace
❌ Relying only on JVM tuning for leaks

cat /u01/ocastomcat/tomcat/apache-tomcat-9.0.65/bin/setenv.sh

#java.awt.headles=strue

export CATALINA_OPTS="$CATALINA_OPTS -Djava.awt.headless=true"

#export CATALINA_OPTS="$CATALINA_OPTS -Xms24576m"

#export CATALINA_OPTS="$CATALINA_OPTS -Xmx24576m"

#export CATALINA_OPTS="$CATALINA_OPTS -Xms8g -Xmx16g"

### ================================

### Memory & Heap Settings

### ================================

export CATALINA_OPTS="$CATALINA_OPTS -Xms32g"

export CATALINA_OPTS="$CATALINA_OPTS -Xmx48g"

# Why? Large application benefits from higher initial heap for stability.

### ================================

### Garbage Collector (G1)

### ================================

export CATALINA_OPTS="$CATALINA_OPTS -XX:+UseG1GC"

export CATALINA_OPTS="$CATALINA_OPTS -XX:MaxGCPauseMillis=200"

export CATALINA_OPTS="$CATALINA_OPTS -XX:+ParallelRefProcEnabled"

### ================================

### Heap Region Tuning (for 16–32GB heaps)

### ================================

export CATALINA_OPTS="$CATALINA_OPTS -XX:G1HeapRegionSize=32m"

### ================================

### Metaspace Tuning (large WAR needs more)

### ================================

export CATALINA_OPTS="$CATALINA_OPTS -XX:MetaspaceSize=512m"

export CATALINA_OPTS="$CATALINA_OPTS -XX:MaxMetaspaceSize=2048m"

### ================================

### JVM Startup Optimization

### ================================

export CATALINA_OPTS="$CATALINA_OPTS -XX:+AlwaysPreTouch"

export CATALINA_OPTS="$CATALINA_OPTS -XX:+DisableExplicitGC"

# --------------------------------

# Heap Dump on OutOfMemoryError

# --------------------------------

export CATALINA_OPTS="$CATALINA_OPTS -XX:+HeapDumpOnOutOfMemoryError"

export CATALINA_OPTS="$CATALINA_OPTS -XX:HeapDumpPath=/u01/ocastomcat/tomcat/apache-tomcat-9.0.65/heapdump"

# --------------------------------

# GC Logging (Java 8 syntax)

# --------------------------------

export CATALINA_OPTS="$CATALINA_OPTS -XX:+PrintGCDetails"

export CATALINA_OPTS="$CATALINA_OPTS -XX:+PrintGCDateStamps"

export CATALINA_OPTS="$CATALINA_OPTS -XX:+PrintTenuringDistribution"

export CATALINA_OPTS="$CATALINA_OPTS -Xloggc:/opt/tomcat/logs/gc.log"

export CATALINA_OPTS="$CATALINA_OPTS -XX:+UseGCLogFileRotation"

export CATALINA_OPTS="$CATALINA_OPTS -XX:NumberOfGCLogFiles=10"

export CATALINA_OPTS="$CATALINA_OPTS -XX:GCLogFileSize=100M"

Example: Production Tomcat (Java 8)

Add to setenv.sh:

export CATALINA_OPTS="
-Xms8g
-Xmx8g
-XX:MetaspaceSize=256m
-XX:MaxMetaspaceSize=512m
-Xss512k
-XX:+UseG1GC
-XX:MaxGCPauseMillis=200
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=/opt/tomcat/heapdump