JVM Profiles

The --profile flag selects a set of optimized JVM flags for your workload.

Available Profiles

server (default)

Standard HotSpot behavior. No additional flags.

Best for:

• Long-running services

• Web servers

• Applications where throughput matters more than startup

Characteristics:

• Full tiered compilation (C1 → C2)

• G1GC (default garbage collector)

• Higher memory overhead

• Peak performance after warmup

cli

Optimized for short-lived processes and CLI tools.

Best for:

• Command-line tools

• Scripts

• One-shot utilities

• Serverless functions

Characteristics:

• Tiered compilation with C1 only (skip C2)

• SerialGC (simpler, faster startup)

• Reduced code cache

• ~200-350ms startup (with AppCDS)

Usage

# CLI profile
jbundle build --input . --output ./dist/app --profile cli

# Server profile (default)
jbundle build --input . --output ./dist/app --profile server

Or in jbundle.toml:

profile = "cli"

JVM Flags

Each profile injects specific JVM flags into the generated binary:

cli

-XX:+TieredCompilation
-XX:TieredStopAtLevel=1
-XX:+UseSerialGC

• TieredStopAtLevel=1: Uses only C1 compiler (fast compilation, no C2 optimization)

• UseSerialGC: Simple single-threaded GC, minimal overhead

server

No additional flags. Uses JVM defaults:

• Full tiered compilation (C1 → C2)

• G1GC garbage collector

Note: Because server adds no GC flags, it's the right choice when you want to specify a custom garbage collector via jvm_args.

Performance Comparison

Metric	cli	server
Startup (cold)	~800-1500ms	~1000-2000ms
Startup (warm)	~200-350ms	~400-600ms
Peak throughput	Lower	Higher
Memory footprint	Lower	Higher
Warmup time	Faster	Slower

When to Use Each

cli profile:
  ✓ Run once and exit
  ✓ Interactive commands
  ✓ Scripts and automation
  ✓ Startup time is critical

server profile:
  ✓ Long-running processes
  ✓ Web servers
  ✓ Background services
  ✓ Throughput is critical

GC Conflict Detection

jbundle automatically detects conflicts between the profile's garbage collector and custom jvm_args.

The cli profile uses -XX:+UseSerialGC. If your jvm_args specifies a different GC (like -XX:+UseZGC or -XX:+UseG1GC), jbundle will emit a warning:

WARN GC conflict: profile 'cli' uses -XX:+UseSerialGC but jvm_args contains -XX:+UseZGC. The JVM cannot use multiple garbage collectors. Consider using profile = "server" or removing -XX:+UseZGC from jvm_args.

The build continues, but the JVM will likely fail at runtime. To fix this, use profile = "server" which doesn't set any GC flags:

# jbundle.toml - using ZGC with server profile
profile = "server"
jvm_args = ["-XX:+UseZGC", "-XX:+UnlockExperimentalVMOptions"]

Combining with AppCDS and CRaC

Profiles work alongside other optimizations:

# CLI + AppCDS (default) → ~200-350ms
jbundle build --input . --output ./app --profile cli

# CLI + CRaC → ~10-50ms (Linux only)
jbundle build --input . --output ./app --profile cli --crac

# Server + no AppCDS → standard JVM startup
jbundle build --input . --output ./app --profile server --no-appcds