Implementation:Apache Kafka Kafka Run Class JVM Options

Knowledge Sources	Apache Kafka
Domains	Operations, JVM_Configuration
Last Updated	2026-02-09 12:00 GMT

Overview

Concrete tool for assembling JVM runtime options for Kafka processes provided by kafka-run-class.sh.

Description

The JVM configuration section of kafka-run-class.sh assembles all Java options from environment variables. It detects the Java version to select appropriate GC logging format, configures JMX for remote monitoring, sets default heap and performance options, and handles debug mode. Each option category uses a separate environment variable with sensible defaults.

Usage

Override individual environment variables before running any Kafka script to customize JVM behavior. The defaults are suitable for development; production deployments should tune heap size and GC settings.

Code Reference

Source Location

Repository: Apache Kafka
File: bin/kafka-run-class.sh
Lines: L201-332

Signature

# Environment variables assembled into JVM options:
# KAFKA_HEAP_OPTS         - Heap size (default: -Xmx256M)
# KAFKA_JVM_PERFORMANCE_OPTS - GC settings (default: G1GC with tuning)
# KAFKA_GC_LOG_OPTS       - GC logging (auto-detected for Java 8 vs 9+)
# KAFKA_JMX_OPTS          - JMX monitoring (enabled when JMX_PORT is set)
# KAFKA_LOG4J_OPTS        - Log4j configuration path
# KAFKA_DEBUG             - Enable Java debug agent
# JAVA_DEBUG_PORT         - Debug agent port (default: 5005)
# KAFKA_OPTS              - Additional JVM options (passthrough)

Import

# Set environment variables before running Kafka:
export KAFKA_HEAP_OPTS="-Xmx6G -Xms6G"
export JMX_PORT=9999
bin/kafka-server-start.sh config/server.properties

I/O Contract

Inputs

Name	Type	Required	Description
KAFKA_HEAP_OPTS	env	No	JVM heap options (default: -Xmx256M)
KAFKA_JVM_PERFORMANCE_OPTS	env	No	GC and performance options
JMX_PORT	env	No	Enable JMX on this port
KAFKA_DEBUG	env	No	Enable Java debug agent
JAVA_HOME	env	No	Java installation path

Outputs

Name	Type	Description
JVM options	string	Complete JVM command-line options for the Java process

Usage Examples

Production Broker Configuration

# Set production heap size
export KAFKA_HEAP_OPTS="-Xmx6G -Xms6G"

# Enable JMX monitoring
export JMX_PORT=9999

# Custom GC settings
export KAFKA_JVM_PERFORMANCE_OPTS="-server -XX:+UseG1GC -XX:MaxGCPauseMillis=20 -XX:InitiatingHeapOccupancyPercent=35"

# Start broker
bin/kafka-server-start.sh config/server.properties

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