my life is short!



Peter Palaga


About me


Projects I build often


Lines of Java Code1 Maven modules2 mvn clean install
Camel Quarkus 93K 1371 23.5 min
Camel 1609K 612 32.6 min
Quarkus 594K 1161 11.1 min


1) cloc --include-lang=Java .
2) mvn clean && find . -type f -name 'pom.xml' | wc -l


Image from imgflip


  • Skipping mojos
  • mvnd a.k.a. Maven Daemon
  • Vertical scaling
  • Incrememental builds with GIB


Why to skip mojos?

  • After pulling from team git repository
  • Source tree in a clean state
  • Checked by the team CI
  • Tests, and various source checks can be skipped

Find candidates for skipping (1/3)


  • A Maven extension
  • Outputs per-mojo per-module exec. times
  • Exec. times not summed up per mojo across modules - limited usefulness
  • An example

Find candidates for skipping (2/3)

Gradle build scans for Maven

  • A Maven extension
  • Allows sorting by execution time
  • An example

Find candidates for skipping (3/3)

async-profiler or any other Java profiler

  • export MAVEN_OPTS="-agentpath:/path/to/, event=cpu,file=mvn-profile.html"
  • Outputs a flame graph
  • Summed mojo execution times are easy to see
mvn clean install -DskipTests -Dformatter.skip -Dimpsort.skip ...
# in Camel Quarkus

All possible skips for this project

$ mvn clean install \
    -DskipTests \
    -Dformatter.skip \
    -Dimpsort.skip \
    -Denforcer.skip \
    -Dcamel-quarkus.update-extension-doc-page.skip \
    -Dskip.installyarn \
    -Dskip.yarn \
    -Dlicense.skip \
    -Dgmaven.execute.skip # underway
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  04:34 min  # down from 23:27 min by mvn clean install -DskipTests
Can we do better?
public class SomeMojo extends AbstractMojo {

    @Parameter(property = "some.skip", defaultValue = "false")
    boolean skip;

    public void execute() {
        if (skip) {
            getLog().info("Skipping as requested by the user");
← What happens before?
  • Resolve and download plugin dependencies
  • Setup a classloader, load the necessary classes
  • Instantiate the Mojo
  • Inject fields (potentially expensive objects)
  • Call Mojo.execute()
How can we avoid all of this?

Remove plugins
from Maven execution plan

    ...                      <!-- Proper skipping -->
            <!-- Only plugins essential for the fast build -->
                    <name>!quickly</name><!-- Active by default unless -Dquickly is passed -->
                    <!-- All other plugins -->


$ mvn clean install -Dquickly
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  04:01 min  # down from 04:34 min by
                               #   mvn clean install -DskipTests -Dformatter.skip ...


Can we do better?

Java is fast *




* When warmed up

Java Warmup costs

  • JVM boot
  • JIT (Just in Time) compilation

Cost of starting Maven

Measurable through a simple experiment:

package org.apache.maven;
public class DefaultMaven implements Maven {
    private MavenExecutionResult doExecute( MavenExecutionRequest request ) {
        System.out.println("End of Maven init: " + System.currentTimeMillis());
        request.setStartTime( new Date() ); // Maven measures from here
$ echo $(($(date +%s%N)/1000000)) && mvn clean install -Dquickly
End of Maven init: 1634117025765
$ echo "$((1634117025765-1634117024986))"
779 # Maven start time in milliseconds

Cost of JIT compilation

mvn clean install -DskipTests -Dformatter.skip -Dimpsort.skip ...
# in Camel Quarkus

Eliminate JVM warm up

  • Have a long living Java process, a.k.a. daemon
  • Pass build requests through a socket
  • Like Gradle daemon, but for Maven

- the Maven Daemon

  • Started by Guillaume Nodet in 2019
  • 24 releases since then
  • Donated to the ASF Maven Project in December 2021


mvnd - how to install

Maven Daemon overview

mvnd - the client

  • GraalVM native executable
  • Looks up a running daemon
    • Or starts a new one
  • Sends a build request via socket
  • Receives events from the daemon
  • Displays the progress



  • Long running Java process
  • Embeds a specific Maven version
    • Does not use any local Maven installation
  • Receives build requests
  • Caches plugin class loaders
  • Exits after a configurable period of time

mvnd speed gains

A build with Many modules
(relatively independent)
cd camel-quarkus && \
   mvn[d] clean install -Dquickly      
    Single module
cd camel-quarkus/extensions-core/core/deployment && \
   mvn[d] clean install \
   -DskipTests             -Dtest=CamelBeansUnremovableTest
mvn baseline       4:01 min 10.11 sec 12.79 sec
mvnd 1st 1:19 (3x) 9.15 (1.1x) 11.82 (1.1x)
mvnd 2nd 1:04 (3.8x) 2.37 (4.3x) 5.26 (2.4x)
mvnd 3rd 1:01 (4x) 1.19 (5.3x) 4.86 (2.6x)
Gains through
  • Class loader caching
    • No repeated JIT
    • Faster JIT-compiled code
  • Parallel execution
  • No JVM boot cost
  • Class loader caching

mvnd - Parallel builds

  • Default number of threads:    Runtime.getRuntime().availableProcessors() - 1
  • -T<n> or -T<n>C supported like with stock Maven

Maven builder

  • Pluggable builder since Maven 3.2.1
  • A strategy for scheduling and building modules
  • singlethreaded (default)
  • multithreaded (with -T)

mvnd - Smart builder

Issues of parallel builds

Hidden dependencies

  •     A
       / \     Maven module dependencies
      B   C    (Lower depends on upper)
       \ /
    No issues with serial builder
  • Possible issues with a parallel builder:
    • C could be reading a file in B's target folder
    • C's test could dynamically read an artifact produced by B from the local Maven repository

Simple remedy: -1/--serial
to force the serial builder

Better remedy:
Make the dependency explicit

Make hidden dependencies explicit


This won't add any real dependency to C but it will guarantee that B is fully built before C

Issues of parallel builds

Local repository access

  • Two modules may download the same artifact concurrently
  • Solved in mvnd 0.7.1
Issues of parallel builds

Broken plugins

Plugins may do nasty things

  • Mutable global state
  • Race conditions

-1/--serial may help

Better: Report/fix the issue in the given plugin

mvnd drawbacks

  • Blocks a few gigs of RAM (configurable)
  • Better not on the CI
  • Windows issues and testing catching up gradualy
  • Class loader caching may have issues in some situations

mvnd --help

$ mvnd --help

usage: mvnd [options] [<goal(s)>] [<phase(s)>]

 -am,--also-make                        If project list is specified, also build projects
                                        required by the list
 -amd,--also-make-dependents            If project list is specified, also build projects
                                        that depend on projects on the list
 -B,--batch-mode                        Run in non-interactive (batch) mode (disables output
 -b,--builder <arg>                     The id of the build strategy to use
 -C,--strict-checksums                  Fail the build if checksums don't match
 -c,--lax-checksums                     Warn if checksums don't match
    --color <arg>                       Defines the color mode of the output. Supported are
                                        'auto', 'always', 'never'.
 -cpu,--check-plugin-updates            Ineffective, only kept for backward compatibility
 -D,--define <arg>                      Define a system property
 -e,--errors                            Produce execution error messages
 -emp,--encrypt-master-password <arg>   Encrypt master security password
 -ep,--encrypt-password <arg>           Encrypt server password
 -f,--file <arg>                        Force the use of an alternate POM file (or directory
                                        with pom.xml)
 -fae,--fail-at-end                     Only fail the build afterwards; allow all
                                        non-impacted builds to continue
 -ff,--fail-fast                        Stop at first failure in reactorized builds
 -fn,--fail-never                       NEVER fail the build, regardless of project result
 -gs,--global-settings <arg>            Alternate path for the global settings file
 -gt,--global-toolchains <arg>          Alternate path for the global toolchains file
 -h,--help                              Display help information
 -l,--log-file <arg>                    Log file where all build output will go (disables
                                        output color)
 -llr,--legacy-local-repository         Use Maven 2 Legacy Local Repository behaviour, ie no
                                        use of _remote.repositories. Can also be activated
                                        by using -Dmaven.legacyLocalRepo=true
 -N,--non-recursive                     Do not recurse into sub-projects
 -npr,--no-plugin-registry              Ineffective, only kept for backward compatibility
 -npu,--no-plugin-updates               Ineffective, only kept for backward compatibility
 -nsu,--no-snapshot-updates             Suppress SNAPSHOT updates
 -ntp,--no-transfer-progress            Do not display transfer progress when downloading or
 -o,--offline                           Work offline
 -P,--activate-profiles <arg>           Comma-delimited list of profiles to activate
 -pl,--projects <arg>                   Comma-delimited list of specified reactor projects
                                        to build instead of all projects. A project can be
                                        specified by [groupId]:artifactId or by its relative
 -q,--quiet                             Quiet output - only show errors
 -r,--resume                            Resume reactor from the last failed project, using
                                        the file in the build directory
    --raw-streams                       Do not decorate output and error streams
 -rf,--resume-from <arg>                Resume reactor from specified project
 -s,--settings <arg>                    Alternate path for the user settings file
 -t,--toolchains <arg>                  Alternate path for the user toolchains file
 -T,--threads <arg>                     Thread count, for instance 2.0C where C is core
 -U,--update-snapshots                  Forces a check for missing releases and updated
                                        snapshots on remote repositories
 -up,--update-plugins                   Ineffective, only kept for backward compatibility
 -v,--version                           Display version information
 -V,--show-version                      Display version information WITHOUT stopping build
 -X,--debug                             Produce execution debug output

mvnd specific options:
 --completion <string>                  Print the completion for the given shell to stdout.
                                        Only --completion bash is supported at this time.
 --purge                                Delete log files under the mvnd.registry directory
                                        that are older than mvnd.logPurgePeriod
 --status                               Prints the status of daemon instances registered in
                                        the registry specified by mvnd.registry
 --stop                                 Stop all daemon instances registered in the
                                        registry specified by mvnd.registry
 -Djava.home=<path>                     Java home for starting the daemon
                                        Env. variable: JAVA_HOME<string>            The JDK_JAVA_OPTIONS option
                                        Env. variable: JDK_JAVA_OPTIONS
 -Dmaven.multiModuleProjectDirectory=<path> The root directory of the current multi module
                                        Maven project
 -Dmaven.repo.local=<path>              The path to the Maven local repository
 -Dmaven.settings=<path>;-s,--settings <path> The location of the maven settings file
 -Dmvnd.buildTime=<boolean>             Log mojos execution time at the end of the build.
 -Dmvnd.builder=<string>;-b,--builder <string> The builder implementation the daemon should
                                        Default: smart
 -Dmvnd.daemonStorage=<path>            The directory under which the daemon stores its
                                        registry, log files, etc. Default:
 -Dmvnd.debug=<boolean>                 If true, the daemon will be launched in debug mode
                                        with the following JVM argument:
                                        otherwise the debug argument is not passed to the
                                        Default: false
 -Dmvnd.duplicateDaemonGracePeriod=<duration> Period after which idle duplicate daemons
                                        will be shut down. Duplicate daemons are daemons
                                        with the same set of discriminating start
                                        Default: 10 seconds
 -Dmvnd.enableAssertions=<boolean>      If true, the -ea option will be passed to the
                                        daemon; otherwise the -ea option is not passed to
                                        the daemon.
                                        Default: false
 -Dmvnd.expirationCheckDelay=<duration> The daemon will check this often whether it should
                                        Default: 10 seconds
 -Dmvnd.home=<path>                     The daemon installation directory. The client
                                        normally sets this according to where its mvnd
                                        executable is located
                                        Env. variable: MVND_HOME
 -Dmvnd.idleTimeout=<duration>          A time period after which an unused daemon will
                                        terminate by itself.
                                        Default: 3 hours
 -Dmvnd.jvmArgs=<string>                Additional JVM args to pass to the daemon
 -Dmvnd.keepAlive=<duration>            If the daemon does not send any message to the
                                        client in this period of time, send a keep-alive
                                        message so that the client knows that the daemon
                                        is still alive.
                                        Default: 100 ms
 -Dmvnd.logPurgePeriod=<duration>       Daemon log files older than this value will be
                                        removed automatically.
                                        Default: 7 days
 -Dmvnd.logback=<path>                  The location of the Logback configuration file the
                                        daemon should use to configure its logging.
 -Dmvnd.maxHeapSize=<memory_size>       The -Xmx value to pass to the daemon
                                        Default: 2G
 -Dmvnd.maxLostKeepAlive=<integer>      The maximum number of keep alive messages that can
                                        be missed by the client before the client
                                        considers the daemon to be dead.
                                        Default: 30
 -Dmvnd.minHeapSize=<memory_size>       The -Xms value to pass to the daemon
                                        Default: 128M
 -Dmvnd.minThreads=<integer>            The minimum number of threads to use when
                                        constructing the default -T parameter for the
                                        daemon. This value is ignored if the user passes
                                        -T, --threads or -Dmvnd.threads on the command
                                        line or if he sets mvnd.threads in
                                        Default: 1
 -Dmvnd.noBuffering=<boolean>           If true the log messages are displayed continuously
                                        like with stock Maven; otherwise buffer the
                                        messages and output at the end of the build,
                                        grouped by module. Passing -B or --batch-mode on
                                        the command line enables this too for the given
                                        Default: false
 -Dmvnd.noDaemon=<boolean>              If true, the client and daemon will run in the same
                                        JVM that exits when the build is finished;
                                        otherwise the client starts/connects to a long
                                        living daemon process. This option is only
                                        available with non-native clients and is useful
                                        mostly for debugging.
                                        Default: false
                                        Env. variable: MVND_NO_DAEMON
 -Dmvnd.pluginRealmEvictPattern=<string> Regexp pattern that will force eviction of the
                                        plugin realms if one of its dependencies matches.
 -Dmvnd.propertiesPath=<path>           The location of the user supplied
                                        Env. variable: MVND_PROPERTIES_PATH
 -Dmvnd.registry=<path>                 The path to the daemon registry. Default:
 -Dmvnd.rollingWindowSize=<integer>     The number of log lines to display for each Maven
                                        module that is built in parallel. The value can be
                                        increased or decreased by pressing + or - key
                                        during the build respectively. This option has no
                                        effect with -Dmvnd.noBuffering=true, -B or
                                        Default: 0
 -Dmvnd.serial;-1,--serial              Use one thread, no log buffering and the default
                                        project builder to behave like a standard maven
                                        Default: false
 -Dmvnd.socketFamily=<string>           Socket family to use
                                        Default: inet
 -Dmvnd.syncContextFactory=<boolean>    The SyncContextFactory to use (can be either 'noop'
                                        or 'ipc' for a server-wide factory).
                                        Default: noop
 -Dmvnd.threads=<string>;-T,--threads <string> The number of threads to pass to the daemon;
                                        same syntax as Maven's -T/--threads option.
 -Dstyle.color=<string>;--color <string> Whether the output should be styled using ANSI
                                        color codes; possible values: auto, always, never
                                        Default: auto
 -Duser.dir=<path>                      The current working directory
 -Duser.home=<path>                     The user home directory

mvnd value types:
 boolean                                true or false; empty string is also interpreted as
                                        true - so -Dmvnd.noBuffering is equivalent to
 duration                               An unlabeled whole number of milliseconds or a
                                        whole number followed by an optional space and a
                                        unit which may be one of the following (in EBNF
                                        notation): d[ay[s]], h[our[s]], m[in[ute[s]]],
                                        s[ec[ond[s]]] or m[illi]s[ec[ond[s]]]. Examples: 7
                                        days, 7days, 7d, 100 milliseconds, 100 millis,
                                        100ms, 100
 integer                                A whole number
 memory_size                            An amount of memory as accepted by the -Xm* family
                                        of HotSpot JVM options. Examples: 1024m, 2g, 5G
 path                                   A local file system path
 string                                 A string

mvnd UI

+/- - reveal/hide rolling log lines for the individual builder threads

CTRL+B - toggle between threaded and rolling views

Vertical scaling

Laptop vs. desktop

A build with Many modules (relatively independent)
cd camel-quarkus && mvn[d] clean install -Dquickly      
Machine Lenovo ThinkPad P1 Gen 3
Core i7 10850H
12 cores
2.7 GHz
    Self made desktop
AMD Ryzen Threadripper 1920X
12 cores, 24 threads
3.5 GHz (1.3x)
mvn       4:01 min 3:42 min (1.1x)
mvnd 1st 1:19 0:55 (1.4x)
mvnd 2nd 1:04 0:42 (1.5x)
mvnd 3rd 1:01 0:40 (1.5x)
Can we do better?

Costs of vertical scaling

Machine Lenovo ThinkPad P1 Gen 3
Core i7 10850H
12 cores
2.7 GHz
    Self made desktop
AMD Ryzen Threadripper 1920X
12 cores, 24 threads
3.5 GHz (1.3x)
Purchase price       2630,- €
(Oct. 2021)
~1300 €
(Feb. 2020, w/out 🖥️ ⌨️ 🖱️)
Power suply unit 135 W 650 W
Idle ~18 W* ~60 W*
Max 129 W* 278 W*
2h work session
(builds, web browsing)
0.06 kWh* 0.21 KWh*
€/year (0.3 €/kWh) 23 € 80 €

*) Measured with a budget power meter from a hobby market

Incremental builds with

Gitflow Incremental Builder


What is GIB?

  • A maven extension
  • Compares the current topic branch with the reference branch
    • typically origin/main or origin/master
  • Build/test only the modules impacted by the change

GIB in Quarkus

Multiple steps to be able run tests on multiple nodes in parallel:

  • Build the whole tree w/out tests and identify impacted modules
  • Calculate test jobs
  • Run test jobs in parallel

Compare the number of tests and execution times per pull request

Wrap up

Techniques to speed up Maven builds

  • Skip unessential mojos
  • Maven daemon to keep the building JVM warm
  • Larger machine
  • Incremental builds with GIB