Native Image Build Output

Build Stages
Resource Usage Statistics
Machine-Readable Build Output
Build Output Options

Here you will find information about the build output of GraalVM Native Image. Below is the example output when building a native executable of the HelloWorld class:

================================================================================
GraalVM Native Image: Generating 'helloworld' (executable)...
================================================================================
[1/7] Initializing...                                            (2.5s @ 0.21GB)
 Version info: 'GraalVM dev Java 11 CE'
 C compiler: gcc (linux, x86_64, 9.3.0)
 Garbage collector: Serial GC
[2/7] Performing analysis...  [*******]                          (5.6s @ 0.46GB)
   2,718 (72.93%) of  3,727 classes reachable
   3,442 (53.43%) of  6,442 fields reachable
  12,128 (44.82%) of 27,058 methods reachable
      27 classes,     0 fields, and   271 methods registered for reflection
      58 classes,    59 fields, and    52 methods registered for JNI access
       4 native libraries: dl, pthread, rt, z
[3/7] Building universe...                                       (0.5s @ 0.61GB)
[4/7] Parsing methods...      [*]                                (0.5s @ 0.86GB)
[5/7] Inlining methods...     [****]                             (0.5s @ 0.73GB)
[6/7] Compiling methods...    [**]                               (3.7s @ 2.38GB)
[7/7] Creating image...                                          (2.1s @ 1.04GB)
   4.00MB (28.31%) for code area:     7,073 compilation units
   5.90MB (41.70%) for image heap:   83,319 objects and 5 resources
   3.24MB (22.91%) for debug info generated in 1.0s
   1.00MB ( 7.08%) for other data
  14.15MB in total
--------------------------------------------------------------------------------
Top 10 packages in code area:           Top 10 object types in image heap:
 632.68KB java.util                      871.62KB byte[] for code metadata
 324.42KB java.lang                      798.53KB java.lang.String
 223.90KB java.util.regex                774.91KB byte[] for general heap data
 221.62KB java.text                      614.06KB java.lang.Class
 198.30KB com.oracle.svm.jni             492.51KB byte[] for java.lang.String
 166.02KB java.util.concurrent           314.81KB java.util.HashMap$Node
 115.44KB java.math                      233.58KB c.o.s.c.h.DynamicHubCompanion
  98.48KB sun.text.normalizer            154.84KB java.lang.String[]
  97.42KB java.util.logging              139.54KB byte[] for embedded resources
  95.18KB c.oracle.svm.core.genscavenge  139.04KB char[]
   1.83MB for 118 more packages            1.29MB for 753 more object types
--------------------------------------------------------------------------------
    0.9s (5.6% of total time) in 17 GCs | Peak RSS: 3.22GB | CPU load: 10.87
--------------------------------------------------------------------------------
Produced artifacts:
 /home/janedoe/helloworld/helloworld (executable)
 /home/janedoe/helloworld/sources (debug_info)
 /home/janedoe/helloworld/helloworld (debug_info)
 /home/janedoe/helloworld/helloworld.build_artifacts.txt
================================================================================
Finished generating 'helloworld' in 16.2s.

Build Stages

Initializing

In this stage, the Native Image build process is set up and Features are initialized.

Native Image Kind

By default, Native Image generates executables but it can also generate native shared libraries and static executables.

Version Info

The version info of the Native Image process. This string is also used for the java.vm.version property within the generated native binary. Please report this version info when you file issues.

Java Version Info

The Java version info (java.runtime.version property) of the Native Image build process. Please report this version info when you file issues.

C Compiler

The C compiler executable, vendor, target architecture, and version info used by the Native Image build process.

Garbage Collector

The garbage collector used within the generated executable:

The Serial GC is the default GC and optimized for low memory footprint and small Java heap sizes.
The G1 GC (only available with GraalVM Enterprise Edition) is a multi-threaded GC that is optimized to reduce stop-the-world pauses and therefore improve latency while achieving high throughput.
The Epsilon GC does not perform any garbage collection and is designed for very short-running applications that only allocate a small amount of memory.

For more information see the docs on Memory Management at Image Run Time.

User-Specific Features

All Features that are either provided or specifically enabled by the user, or implicitly registered for the user, for example, by a framework. GraalVM Native Image deploys a number of internal features, which are excluded from this list.

Performing Analysis

In this stage, a points-to analysis is performed. The progress indicator visualizes the number of analysis iterations. A large number of iterations can indicate problems in the analysis likely caused by misconfiguration or a misbehaving feature.

Reachable Classes, Fields, and Methods

The number of classes, fields, and methods that are reachable versus the total number of classes and methods loaded as part of the build process. A significantly larger number of loaded classes that are not reachable can indicate a configuration problem. To reduce overhead, please ensure that the classpath only contains entries that are needed for building the application.

Reflection Registrations

The number of classes, fields, and methods that are registered for reflection. Large numbers can cause significant reflection overheads, slow down the build process, and increase the size of the native binary (see reflection metadata).

JNI Access Registrations

The number of classes, fields, and methods that are registered for JNI access.

Runtime Compiled Methods

The number of methods marked for runtime compilation. This number is only shown if runtime compilation is built into the executable, for example, when building a Truffle language. Runtime-compiled methods account for graph encodings in the heap.

Building Universe

In this stage, a universe with all classes, fields, and methods is built, which is then used to create the native binary.

Parsing Methods

In this stage, the Graal compiler parses all reachable methods. The progress indicator is printed periodically at an increasing interval.

Inlining Methods

In this stage, trivial method inlining is performed. The progress indicator visualizes the number of inlining iterations.

Compiling Methods

In this stage, the Graal compiler compiles all reachable methods to machine code. The progress indicator is printed periodically at an increasing interval.

Creating Image

In this stage, the native binary is created and written to disk. Debug info is also generated as part of this stage (if requested).

Code Area

The code area contains machine code produced by the Graal compiler for all reachable methods. Therefore, reducing the number of reachable methods also reduces the size of the code area.

Image Heap

The heap contains reachable objects such as static application data, metadata, and byte[] for different purposes (see below).

General Heap Data Stored in `byte[]`

The total size of all byte[] objects that are neither used for java.lang.String, nor code metadata, nor reflection metadata, nor graph encodings. Therefore, this can also include byte[] objects from application code.

Embedded Resources Stored in `byte[]`

The total size of all byte[] objects used for storing resources (for example, files accessed via Class.getResource()) within the native binary. The number of resources is shown in the Heap section.

Code Metadata Stored in `byte[]`

The total size of all byte[] objects used for metadata for the code area. Therefore, reducing the number of reachable methods also reduces the size of this metadata.

Reflection Metadata Stored in `byte[]`

The total size of all byte[] objects used for reflection metadata, including class, field, method, and constructor data. To reduce the amount of reflection metadata, reduce the number of elements registered for reflection.

Graph Encodings Stored in `byte[]`

The total size of all byte[] objects used for graph encodings. These encodings are a result of runtime compiled methods. Therefore, reducing the number of such methods also reduces the size of corresponding graph encodings.

Debug Info

The total size of generated debug information (if enabled).

Other Data

The amount of data in the binary that is neither in the code area, nor in the heap, nor debug info. This data typically contains internal information for Native Image and should not be dominating.

Resource Usage Statistics

Garbage Collections

The total time spent in all garbage collectors, total GC time divided by the total process time as a percentage, and the total number of garbage collections. A large number of collections or time spent in collectors usually indicates that the system is under memory pressure. Increase the amount of available memory to reduce the time to build the native binary.

Peak RSS

Peak resident set size as reported by the operating system. This value indicates the maximum amount of memory consumed by the build process. If the GC statistics do not show any problems, the amount of available memory of the system can be reduced to a value closer to the peak RSS.

CPU load

The CPU time used by the process divided by the total process time. Increase the number of CPU threads to reduce the time to build the native binary.

Build Output Options

Run native-image --expert-options-all | grep "BuildOutput" to see all build output options:

-H:±BuildOutputBreakdowns    Show code and heap breakdowns as part of the build output. Default: + (enabled).
-H:±BuildOutputColorful      Colorize build output. Default: + (enabled).
-H:±BuildOutputGCWarnings    Print GC warnings as part of build output. Default: + (enabled).
-H:±BuildOutputLinks         Show links in build output. Default: + (enabled).
-H:±BuildOutputPrefix        Prefix build output with '<pid>:<name of binary>'. Default: - (disabled).
-H:±BuildOutputProgress      Report progress in build output. Default: + (enabled).