Cassandra JVM Options

Configure JVM settings for optimal Cassandra performance.

Configuration Files

JDK Version	File
JDK 11+	jvm11-server.options
JDK 17+	jvm17-server.options

Location: /etc/cassandra/

Heap Configuration

# jvm11-server.options

# Set heap size (same for min and max)
-Xms16G
-Xmx16G

# Guidelines:
# - Max 31GB (compressed oops)
# - 1/4 of total RAM typically
# - Leave room for OS page cache

Heap Sizing Guidelines

RAM	Heap Size	Notes
8GB	4GB	Development
32GB	8GB	Small production
64GB	16GB	Standard production
128GB+	31GB	Max recommended

Garbage Collection

G1GC (Recommended)

-XX:+UseG1GC
-XX:MaxGCPauseMillis=500
-XX:InitiatingHeapOccupancyPercent=70
-XX:ParallelGCThreads=16
-XX:ConcGCThreads=4
-XX:+ParallelRefProcEnabled

ZGC (JDK 17+)

-XX:+UseZGC
-XX:SoftMaxHeapSize=28G
# -XX:+ZGenerational  # JDK 21+ only, improves GC efficiency

GC Logging

# JDK 11+
-Xlog:gc*:file=/var/log/cassandra/gc.log:time,uptime:filecount=10,filesize=10M

Memory Settings

# Metaspace
-XX:MetaspaceSize=128M
-XX:MaxMetaspaceSize=256M

# Direct memory (off-heap)
-XX:MaxDirectMemorySize=4G

# String deduplication
-XX:+UseStringDeduplication

Performance Options

# Disable explicit GC calls
-XX:+DisableExplicitGC

# Large pages (if enabled in OS)
-XX:+UseLargePages

# Thread stack size
-Xss256k

Debug Options

# Heap dump on OOM
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=/var/lib/cassandra/

# Print GC details (JDK 8 style for reference)
# Deprecated in JDK 11+, use Xlog instead

Complete Example

# /etc/cassandra/jvm11-server.options

# Heap
-Xms16G
-Xmx16G

# GC
-XX:+UseG1GC
-XX:MaxGCPauseMillis=500
-XX:InitiatingHeapOccupancyPercent=70

# GC Logging
-Xlog:gc*:file=/var/log/cassandra/gc.log:time,uptime:filecount=10,filesize=10M

# Metaspace
-XX:MetaspaceSize=128M
-XX:MaxMetaspaceSize=256M

# Error handling
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=/var/lib/cassandra/

# Performance
-XX:+DisableExplicitGC
-XX:+UseStringDeduplication

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Next Steps

• cassandra.yaml - Main configuration
• Performance Tuning - Optimization
• Monitoring - JVM monitoring