JVM Heap, GC, and Connector Tuning for Tomcat 10.1

JDK 17 LTS Baseline

ColdFusion 2025 recommends JDK 17 LTS for optimal performance and security. Verify your Java version:

java -version

JVM Configuration File

Edit the JVM configuration file to adjust heap size and garbage collection settings:

• Linux: /opt/coldfusion/cfusion/bin/jvm.config
• Windows: C:\ColdFusion2025\cfusion\bin\jvm.config

Baseline JVM Flags

Add these flags to your jvm.config file for optimal performance:

# Security and entropy
-Djava.security.egd=file:/dev/urandom

# G1 Garbage Collector (recommended)
-XX:+UseG1GC
-XX:MaxGCPauseMillis=200
-XX:+ParallelRefProcEnabled
-XX:+AlwaysPreTouch

# Heap dump on OOM
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=/opt/coldfusion/heapdumps

# GC Logging
-Xlog:gc*:file=/opt/coldfusion/logs/gc.log:time,uptime:filecount=5,filesize=20M

Heap Sizing Guidelines

Size your heap based on your application's memory requirements. Follow these guidelines to ensure optimal performance:

• Start with 1x your application's live set plus 30% headroom for growth
• Maintain at least 30% free heap during normal operation
• Prevent heap from reaching 70% capacity, as this triggers more frequent garbage collection cycles
• Set the minimum (-Xms) and maximum (-Xmx) heap to the same value to prevent dynamic resizing overhead

# Example: 4GB heap
-Xms4096m
-Xmx4096m

Garbage Collector Options

ColdFusion 2025 supports multiple garbage collectors:

• G1 GC (Recommended): Balanced throughput and pause times, good for most workloads
• Parallel GC: High throughput, longer pause times
• ZGC: Ultra-low latency, requires JDK 17+, experimental for CF

Tomcat Connector Tuning

Edit the server.xml file to tune Tomcat connectors. The following are key settings you can configure in the Connector element:

<Connector port="8500"
           protocol="HTTP/1.1"
           maxThreads="200"
           acceptCount="100"
           connectionTimeout="20000"
           keepAliveTimeout="15000"
           maxKeepAliveRequests="100" />

• maxThreads: Maximum number of concurrent requests to handle (tune this based on your RPS and PMT data)
• acceptCount: Queue size for incoming requests when all threads are busy
• connectionTimeout: Number of milliseconds to wait for a request before timing out
• keepAliveTimeout: Number of seconds to keep idle connections alive before closing them

TLS Configuration

Disable legacy TLS versions and use modern cipher suites:

<Connector port="8500"
           protocol="org.apache.coyote.http11.Http11NioProtocol"
           SSLEnabled="true"
           sslProtocol="TLS"
           sslEnabledProtocols="TLSv1.2,TLSv1.3" />