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      Interfaces
    </label>
    <nav class="md-nav" data-md-component="collapsible" data-md-level="2">
      <label class="md-nav__title" for="nav-11-4">
        Interfaces
      </label>
      <ul class="md-nav__list" data-md-scrollfix>
        
        
  <li class="md-nav__item">
    <a href="../interface_jvmti/" title="JVMTI" class="md-nav__link">
      JVMTI
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../interface_dtfj/" title="DTFJ" class="md-nav__link">
      DTFJ
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../interface_lang_management/" title="Language Management" class="md-nav__link">
      Language Management
    </a>
  </li>

        
      </ul>
    </nav>
  </li>

        
      </ul>
    </nav>
  </li>

    
  <li class="md-nav__item md-nav__item--nested">
    
      <input class="md-toggle md-nav__toggle" data-md-toggle="nav-12" type="checkbox" id="nav-12">
    
    <label class="md-nav__link" for="nav-12">
      Command-line options
    </label>
    <nav class="md-nav" data-md-component="collapsible" data-md-level="1">
      <label class="md-nav__title" for="nav-12">
        Command-line options
      </label>
      <ul class="md-nav__list" data-md-scrollfix>
        
        
  <li class="md-nav__item">
    <a href="../cmdline_specifying/" title="Specifying options" class="md-nav__link">
      Specifying options
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../cmdline_general/" title="Standard options" class="md-nav__link">
      Standard options
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../cmdline_migration/" title="Switching to OpenJ9" class="md-nav__link">
      Switching to OpenJ9
    </a>
  </li>

        
  <li class="md-nav__item md-nav__item--nested">
    
      <input class="md-toggle md-nav__toggle" data-md-toggle="nav-12-4" type="checkbox" id="nav-12-4">
    
    <label class="md-nav__link" for="nav-12-4">
      System property options
    </label>
    <nav class="md-nav" data-md-component="collapsible" data-md-level="2">
      <label class="md-nav__title" for="nav-12-4">
        System property options
      </label>
      <ul class="md-nav__list" data-md-scrollfix>
        
        
  <li class="md-nav__item">
    <a href="../d_jvm_commands/" title="Using System properties" class="md-nav__link">
      Using System properties
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmenableclasscaching/" title="-Dcom.ibm.enableClassCaching" class="md-nav__link">
      -Dcom.ibm.enableClassCaching
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmenablelegacydumpsecurity/" title="-Dcom.ibm.enableLegacyDumpSecurity" class="md-nav__link">
      -Dcom.ibm.enableLegacyDumpSecurity
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmenablelegacylogsecurity/" title="-Dcom.ibm.enableLegacyLogSecurity" class="md-nav__link">
      -Dcom.ibm.enableLegacyLogSecurity
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmenablelegacytracesecurity/" title="-Dcom.ibm.enableLegacyTraceSecurity" class="md-nav__link">
      -Dcom.ibm.enableLegacyTraceSecurity
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmgpudisable/" title="-Dcom.ibm.gpu.disable" class="md-nav__link">
      -Dcom.ibm.gpu.disable
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmgpuenable/" title="-Dcom.ibm.gpu.enable" class="md-nav__link">
      -Dcom.ibm.gpu.enable
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmgpuverbose/" title="-Dcom.ibm.gpu.verbose" class="md-nav__link">
      -Dcom.ibm.gpu.verbose
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmlangmanagementosmxbeaniscputime100ns/" title="-Dcom.ibm.lang.management.OperatingSystemMXBean.isCpuTime100ns" class="md-nav__link">
      -Dcom.ibm.lang.management.OperatingSystemMXBean.isCpuTime100ns
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmlangmanagementverbose/" title="-Dcom.ibm.lang.management.verbose" class="md-nav__link">
      -Dcom.ibm.lang.management.verbose
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmtoolsattachdirectory/" title="-Dcom.ibm.tools.attach.directory" class="md-nav__link">
      -Dcom.ibm.tools.attach.directory
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmtoolsattachdisplayname/" title="-Dcom.ibm.tools.attach.displayName" class="md-nav__link">
      -Dcom.ibm.tools.attach.displayName
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmtoolsattachenable/" title="-Dcom.ibm.tools.attach.enable" class="md-nav__link">
      -Dcom.ibm.tools.attach.enable
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmtoolsattachid/" title="-Dcom.ibm.tools.attach.id" class="md-nav__link">
      -Dcom.ibm.tools.attach.id
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dcomibmtoolsattachtimeout/" title="-Dcom.ibm.tools.attach.timeout" class="md-nav__link">
      -Dcom.ibm.tools.attach.timeout
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../dfileencoding/" title="-Dfile.encoding" class="md-nav__link">
      -Dfile.encoding
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../djavacompiler/" title="-Djava.compiler" class="md-nav__link">
      -Djava.compiler
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../djavalangstringsubstringnocopy/" title="-Djava.lang.string.substring.nocopy" class="md-nav__link">
      -Djava.lang.string.substring.nocopy
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../djavalangstringbuffergrowaggressively/" title="-Djava.lang.stringBuffer.growAggressively" class="md-nav__link">
      -Djava.lang.stringBuffer.growAggressively
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../djdknativecbc/" title="-Djdk.nativeCBC" class="md-nav__link">
      -Djdk.nativeCBC
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../djdknativechacha20/" title="-Djdk.nativeChaCha20" class="md-nav__link">
      -Djdk.nativeChaCha20
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../djdknativecrypto/" title="-Djdk.nativeCrypto" class="md-nav__link">
      -Djdk.nativeCrypto
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../djdknativedigest/" title="-Djdk.nativeDigest" class="md-nav__link">
      -Djdk.nativeDigest
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../djdknativegcm/" title="-Djdk.nativeGCM" class="md-nav__link">
      -Djdk.nativeGCM
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../djdknativersa/" title="-Djdk.nativeRSA" class="md-nav__link">
      -Djdk.nativeRSA
    </a>
  </li>

        
      </ul>
    </nav>
  </li>

        
  <li class="md-nav__item md-nav__item--nested">
    
      <input class="md-toggle md-nav__toggle" data-md-toggle="nav-12-5" type="checkbox" id="nav-12-5">
    
    <label class="md-nav__link" for="nav-12-5">
      JVM -X options
    </label>
    <nav class="md-nav" data-md-component="collapsible" data-md-level="2">
      <label class="md-nav__title" for="nav-12-5">
        JVM -X options
      </label>
      <ul class="md-nav__list" data-md-scrollfix>
        
        
  <li class="md-nav__item">
    <a href="../x_jvm_commands/" title="Using -X options" class="md-nav__link">
      Using -X options
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../x/" title="-X" class="md-nav__link">
      -X
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xaggressive/" title="-Xaggressive" class="md-nav__link">
      -Xaggressive
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xalwaysclassgc/" title="-Xalwaysclassgc" class="md-nav__link">
      -Xalwaysclassgc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xaot/" title="-Xaot" class="md-nav__link">
      -Xaot
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xargencoding/" title="-Xargencoding" class="md-nav__link">
      -Xargencoding
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xbootclasspath/" title="-Xbootclasspath" class="md-nav__link">
      -Xbootclasspath
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xceehdlr/" title="-XCEEHDLR" class="md-nav__link">
      -XCEEHDLR
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xcheck/" title="-Xcheck" class="md-nav__link">
      -Xcheck
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xclassgc/" title="-Xclassgc" class="md-nav__link">
      -Xclassgc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xcodecache/" title="-Xcodecache" class="md-nav__link">
      -Xcodecache
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xcodecachetotal/" title="-Xcodecachetotal" class="md-nav__link">
      -Xcodecachetotal
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xcomp/" title="-Xcomp" class="md-nav__link">
      -Xcomp
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xcompactexplicitgc/" title="-Xcompactexplicitgc" class="md-nav__link">
      -Xcompactexplicitgc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xcompactgc/" title="-Xcompactgc" class="md-nav__link">
      -Xcompactgc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xcompilationthreads/" title="-XcompilationThreads" class="md-nav__link">
      -XcompilationThreads
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xcompressedrefs/" title="-Xcompressedrefs" class="md-nav__link">
      -Xcompressedrefs
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xconcurrentbackground/" title="-Xconcurrentbackground" class="md-nav__link">
      -Xconcurrentbackground
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xconcurrentlevel/" title="-Xconcurrentlevel" class="md-nav__link">
      -Xconcurrentlevel
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xconcurrentslack/" title="-Xconcurrentslack" class="md-nav__link">
      -Xconcurrentslack
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xconmeter/" title="-Xconmeter" class="md-nav__link">
      -Xconmeter
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xenableexcessivegc/" title="-Xdisableexcessivegc" class="md-nav__link">
      -Xdisableexcessivegc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xenableexplicitgc/" title="-Xdisableexplicitgc" class="md-nav__link">
      -Xdisableexplicitgc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xdisablejavadump/" title="-Xdisablejavadump" class="md-nav__link">
      -Xdisablejavadump
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xenablestringconstantgc/" title="-Xdisablestringconstantgc" class="md-nav__link">
      -Xdisablestringconstantgc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xdump/" title="-Xdump" class="md-nav__link">
      -Xdump
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xenableexcessivegc/" title="-Xenableexcessivegc" class="md-nav__link">
      -Xenableexcessivegc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xenableexplicitgc/" title="-Xenableexplicitgc" class="md-nav__link">
      -Xenableexplicitgc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xenablestringconstantgc/" title="-Xenablestringconstantgc" class="md-nav__link">
      -Xenablestringconstantgc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xfastresolve/" title="-Xfastresolve" class="md-nav__link">
      -Xfastresolve
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xfuture/" title="-Xfuture" class="md-nav__link">
      -Xfuture
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xgc/" title="-Xgc" class="md-nav__link">
      -Xgc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xgcsplitheap/" title="-Xgc:splitheap" class="md-nav__link">
      -Xgc:splitheap
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xgcpolicy/" title="-Xgcpolicy" class="md-nav__link">
      -Xgcpolicy
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xgcthreads/" title="-Xgcthreads" class="md-nav__link">
      -Xgcthreads
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xgcworkpackets/" title="-Xgcworkpackets" class="md-nav__link">
      -Xgcworkpackets
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xifa/" title="-Xifa" class="md-nav__link">
      -Xifa
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xint/" title="-Xint" class="md-nav__link">
      -Xint
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xss/" title="-Xiss" class="md-nav__link">
      -Xiss
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xjit/" title="-Xjit" class="md-nav__link">
      -Xjit
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xjni/" title="-Xjni" class="md-nav__link">
      -Xjni
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xlinenumbers/" title="-Xlinenumbers" class="md-nav__link">
      -Xlinenumbers
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xloa/" title="-Xloa" class="md-nav__link">
      -Xloa
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xloaminimum/" title="-Xloainitial" class="md-nav__link">
      -Xloainitial
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xloaminimum/" title="-Xloamaximum" class="md-nav__link">
      -Xloamaximum
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xloaminimum/" title="-Xloaminimum" class="md-nav__link">
      -Xloaminimum
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xlockreservation/" title="-XlockReservation" class="md-nav__link">
      -XlockReservation
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xlockword/" title="-Xlockword" class="md-nav__link">
      -Xlockword
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xlog/" title="-Xlog" class="md-nav__link">
      -Xlog
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xlp/" title="-Xlp" class="md-nav__link">
      -Xlp
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xlpcodecache/" title="-Xlp:codecache" class="md-nav__link">
      -Xlp:codecache
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xlpobjectheap/" title="-Xlp:objectheap" class="md-nav__link">
      -Xlp:objectheap
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmine/" title="-Xmaxe" class="md-nav__link">
      -Xmaxe
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xminf/" title="-Xmaxf" class="md-nav__link">
      -Xmaxf
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmint/" title="-Xmaxt" class="md-nav__link">
      -Xmaxt
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmca/" title="-Xmca" class="md-nav__link">
      -Xmca
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmca/" title="-Xmco" class="md-nav__link">
      -Xmco
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmcrs/" title="-Xmcrs" class="md-nav__link">
      -Xmcrs
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmine/" title="-Xmine" class="md-nav__link">
      -Xmine
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xminf/" title="-Xminf" class="md-nav__link">
      -Xminf
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmint/" title="-Xmint" class="md-nav__link">
      -Xmint
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmn/" title="-Xmn" class="md-nav__link">
      -Xmn
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmn/" title="-Xmns" class="md-nav__link">
      -Xmns
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmn/" title="-Xmnx" class="md-nav__link">
      -Xmnx
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmo/" title="-Xmo" class="md-nav__link">
      -Xmo
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmo/" title="-Xmoi" class="md-nav__link">
      -Xmoi
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmo/" title="-Xmos" class="md-nav__link">
      -Xmos
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmo/" title="-Xmox" class="md-nav__link">
      -Xmox
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmr/" title="-Xmr" class="md-nav__link">
      -Xmr
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmr/" title="-Xmrx" class="md-nav__link">
      -Xmrx
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xms/" title="-Xms" class="md-nav__link">
      -Xms
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xmso/" title="-Xmso" class="md-nav__link">
      -Xmso
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xms/" title="-Xmx" class="md-nav__link">
      -Xmx
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xaot/" title="-Xnoaot" class="md-nav__link">
      -Xnoaot
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xclassgc/" title="-Xnoclassgc" class="md-nav__link">
      -Xnoclassgc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xcompactexplicitgc/" title="-Xnocompactexplicitgc" class="md-nav__link">
      -Xnocompactexplicitgc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xcompactgc/" title="-Xnocompactgc" class="md-nav__link">
      -Xnocompactgc
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xcompressedrefs/" title="-Xnocompressedrefs" class="md-nav__link">
      -Xnocompressedrefs
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xjit/" title="-Xnojit" class="md-nav__link">
      -Xnojit
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xlinenumbers/" title="-Xnolinenumbers" class="md-nav__link">
      -Xnolinenumbers
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xloa/" title="-Xnoloa" class="md-nav__link">
      -Xnoloa
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xsigcatch/" title="-Xnosigcatch" class="md-nav__link">
      -Xnosigcatch
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xsigchain/" title="-Xnosigchain" class="md-nav__link">
      -Xnosigchain
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xnumanone/" title="-Xnuma:none" class="md-nav__link">
      -Xnuma:none
    </a>
  </li>

        
  <li class="md-nav__item">
    <a href="../xoptionsfile/" title="-Xoptionsfile" class="md-nav__link">
      -Xoptionsfile
    </a>
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<h1 id="getting-started-with-openj9">Getting started with OpenJ9</h1>
<p>OpenJ9 is a high performance, scalable, Java&trade; virtual machine (VM) implementation that is fully compliant with the <a href="https://docs.oracle.com/javase/specs/index.html">Java Virtual Machine Specification</a>.</p>
<p>At run time, the VM interprets the Java bytecode that is compiled by the Java compiler. The VM acts as a translator between the language and the underlying operating system and hardware. A Java program requires a specific VM to run on a particular platform, such as Linux&reg;, z/OS&reg;, or Windows&trade;.</p>
<p>This reference material provides information about the VM configuration and tuning options, together with the default settings.</p>
<h2 id="configuring-your-system">Configuring your system</h2>
<p>For normal operation, certain environment variables must be set at the operating system level. Depending on your system environment, you might also want to set other configuration options that allow the VM to exploit hardware and operating system features. Read <a href="https://www.ibm.com/support/knowledgecenter/SSYKE2_8.0.0/com.ibm.java.vm.80.doc/docs/j9_configure.html">Customizing your system</a> to learn more about the following options:</p>
<ul>
<li>Setting the PATH and CLASSPATH environment variable.</li>
<li>Setting the LIBPATH or LD_LIBRARY_PATH environment variable (AIX&reg; and Linux) to indicate where to find shared libraries.</li>
<li>Setting ulimits on AIX and Linux systems to ensure that the operating system allocates sufficient resources for your application.</li>
<li>Setting region size, BPXPRM parameters, and Language Environment&reg; runtime options on z/OS systems.</li>
<li>If your application allocates a large amount of memory and frequently accesses that memory, you might want to enable large page support on your system. See <a href="https://www.ibm.com/support/knowledgecenter/SSYKE2_8.0.0/com.ibm.java.vm.80.doc/docs/j9_configure_large_page.html">Configuring large page memory allocation</a>.</li>
<li>Configuring Dynamic LPAR support on AIX systems.</li>
</ul>
<p><i class="fa fa-pencil-square-o" aria-hidden="true"></i> <strong>Note:</strong> On macOS&reg; systems, you must set the DYLD_LIBRARY_PATH environment variable to indicate where to find shared libraries. In addition, to ensure there are sufficient resources for your application, you might need to increase system limits by using <code>launchctl</code>, <code>ulimit</code>, or <code>kern.&lt;VARIABLES&gt;</code>. For further instructions, refer to the documentation for your macOS release.</p>
<h2 id="performance-tuning">Performance tuning</h2>
<p>OpenJ9 is configured to start with a set of default options that provide the optimal runtime environment for Java applications with typical workloads. However, if your application is atypical, you can improve performance by tuning the OpenJ9 VM. You can also improve performance by enabling hardware features or using specific APIs in your application code.</p>
<h3 id="garbage-collection-policies">Garbage collection policies</h3>
<p>OpenJ9 includes several garbage collection policies. To learn more about these policies and the types of application workload that can benefit from them, see <a href="../gc/">Garbage Collection</a>.</p>
<h3 id="class-data-sharing">Class data sharing</h3>
<p>You can share class data between running VMs, which can reduce the startup time for a VM once the cache has been created. For more information, see <a href="../shrc/">Class Data Sharing</a>.</p>
<h3 id="native-data-operations">Native data operations</h3>
<p>If your Java application manipulates native data, consider writing your application to take advantage of methods in the Data Access Accelerator API.</p>
<h3 id="cloud-optimizations">Cloud optimizations</h3>
<p>To improve the performance of applications that run in containers, try setting the following tuning options:</p>
<ul>
<li>Use a shared classes cache (<code>-Xshareclasses -XX:SharedCacheHardLimit=200m -Xscmx60m</code>) with Ahead-Of-Time (AOT) compilation to improve your startup time. For more information, see <a href="../shrc/">Class Data Sharing</a> and <a href="../aot/">AOT Compiler</a>.</li>
<li>Use the <a href="../xtunevirtualized/">-Xtune:virtualized</a> option, which configures OpenJ9 for typical cloud deployments where VM guests are provisioned with a small number of virtual CPUs to maximize the number of applications that can be run. When enabled, OpenJ9 adapts its internal processes to reduce the amount of CPU consumed and trim down the memory footprint. These changes come at the expense of only a small loss in throughput.</li>
</ul>
<p>The OpenJ9 VM automatically detects when it is running in a docker container and uses a mechanism to detect when the VM is idle. When an idle state is detected, OpenJ9 runs a garbage collection cycle and releases free memory pages back to the operating system. The object heap is also compacted to make best use of the available memory for further application processing. For cloud services that charge based on memory usage, maintaining a small footprint can generate cost savings. For more information about tuning options that control this process, see <a href="../xxidletuningminidlewaittime/">-XX:IdleTuningMinIdleWaitTime</a>.</p>
<h3 id="cryptographic-operations">Cryptographic operations</h3>
<p>OpenJDK uses the in-built Java cryptographic implementation by default. However, native cryptographic implementations
typically provide better performance. OpenSSL is a native open source cryptographic toolkit for Transport Layer Security (TLS) and
Secure Sockets Layer (SSL) protocols, which is well established and used with many enterprise applications. The OpenSSL V1.0.x and V1.1.x implementations are currently supported for the Digest, CBC, GCM, and RSA algorithms. The OpenSSL V1.1.x implementation is also supported for the ChaCha20 and ChaCha20-Poly1305 algorithms.</p>
<p>On Linux and AIX platforms, the OpenSSL 1.0.x or 1.1.x library is expected to be found on the system path. If you use a package manager to install OpenSSL, the system path will be updated automatically. On other platforms, the OpenSSL 1.1.x library is currently bundled with the binaries from AdoptOpenJDK.</p>
<p>OpenSSL support is enabled by default for all supported algorithms. If you want to limit support to specific algorithms, a number of
system properties are available for tuning the implementation.</p>
<p>Each algorithm can be disabled individually by setting the following system properties on the command line:</p>
<ul>
<li>To turn off <strong>Digest</strong>, set <code>-Djdk.nativeDigest=false</code></li>
<li>To turn off <strong>ChaCha20</strong> and <strong>ChaCha20-Poly1305</strong>, set <code>-Djdk.nativeChaCha20=false</code>. <i class="fa fa-pencil-square-o" aria-hidden="true"></i> <strong>Note:</strong> <img alt="Start of content that applies to Java 8 (LTS)" src="../cr/java8.png" /> These algorithms are not supported on Java 8 <img alt="End of content that applies only to Java 8 (LTS)" src="../cr/java_close_lts.png" /></li>
<li>To turn off <strong>CBC</strong>, set <code>-Djdk.nativeCBC=false</code></li>
<li>To turn off <strong>GCM</strong>, set <code>-Djdk.nativeGCM=false</code></li>
<li>To turn off <strong>RSA</strong>, set <code>-Djdk.nativeRSA=false</code></li>
</ul>
<p>You can turn off all the algorithms by setting the following system property on the command line:</p>
<pre><code>-Djdk.nativeCrypto=false
</code></pre>

<p>To build a version of OpenJDK with OpenJ9 that includes OpenSSL support, follow the steps in our detailed build instructions:</p>
<ul>
<li><a href="https://github.com/eclipse/openj9/blob/master/doc/build-instructions/Build_Instructions_V8.md">OpenJDK 8 with OpenJ9</a>.</li>
<li><a href="https://github.com/eclipse/openj9/blob/master/doc/build-instructions/Build_Instructions_V11.md">OpenJDK 11 with OpenJ9</a>.</li>
<li><a href="https://github.com/eclipse/openj9/blob/master/doc/build-instructions/Build_Instructions_V14.md">OpenJDK 14 with OpenJ9</a>.</li>
</ul>
<p><i class="fa fa-pencil-square-o" aria-hidden="true"></i> <strong>Note:</strong> If you obtain an OpenJDK with OpenJ9 build from <a href="https://adoptopenjdk.net/">AdoptOpenJDK</a> that includes OpenSSL or build a version yourself that includes OpenSSL support, the following acknowledgements apply in accordance with the license terms:</p>
<ul>
<li><em>This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit. (http://www.openssl.org/).</em></li>
<li><em>This product includes cryptographic software written by Eric Young (eay@cryptsoft.com).</em></li>
</ul>
<h3 id="exploiting-gpus">Exploiting GPUs</h3>
<p>OpenJ9 provides the <a href="https://www.ibm.com/support/knowledgecenter/SSYKE2_8.0.0/com.ibm.java.api.80.doc/com.ibm.cuda/index.html?view=kc">CUDA4J API</a> and the <a href="https://www.ibm.com/support/knowledgecenter/SSYKE2_8.0.0/com.ibm.java.api.80.doc/com.ibm.gpu/index.html?view=kc">com.ibm.gpu API</a>, which allow you to develop applications that can take advantage of graphics processing unit (GPU) processing for suitable functions, such as code page conversion. You can also enable the JIT compiler to offload certain processing tasks to a GPU by specifying the <code>-Xjit:enableGPU</code> option on the command line. When enabled, the JIT compiler determines when to offload tasks based on performance heuristics.</p>
<p>GPU processing is supported only on Windows (x86-64) and Linux (x86-64 and IBM Power LE) systems. For more information about enabling GPU processing, see <a href="https://www.ibm.com/support/knowledgecenter/SSYKE2_8.0.0/com.ibm.java.vm.80.doc/docs/gpu_overview.html">Exploiting graphics processing units</a>.</p>
<p>Special consideration is needed when using the WDDM driver model for GPUs on Windows. Using the WDDM driver model means the GPU is also used as a display device and as such is subject to the <a href="https://docs.microsoft.com/en-us/windows-hardware/drivers/display/timeout-detection-and-recovery">Timeout Detection and Recovery (TDR) mechanism</a> of Windows. If you are running demanding GPU workloads, you should increase the timeout from the default 2 seconds. More detail may be found in <a href="https://docs.nvidia.com/cuda/cuda-installation-guide-microsoft-windows/index.html#driver-model">NVIDIA's Installation Guide for Windows</a>.</p>
<h2 id="runtime-options">Runtime options</h2>
<p>Runtime options are specified on the command line and include system properties, standard options, nonstandard (<strong>-X</strong>) options, and <strong>-XX</strong> options. For a detailed list of runtime options, see <a href="../cmdline_specifying/">OpenJ9 command-line options</a></p>
<h2 id="default-settings">Default settings</h2>
<p>If you do not specify any options on the command line at run time, the OpenJ9 VM starts with default settings that define how it operates. For more information about these settings, see <a href="../openj9_defaults/">Default settings for the OpenJ9 VM</a>.</p>
<h2 id="using-jlink"><img alt="Start of content that applies to Java 11 (LTS) and later" src="../cr/java11plus.png" /> Using Jlink</h2>
<p>On Java 11 and later, you can use the <code>jlink</code> utility to create a custom OpenJ9 runtime image, which allows you to optimize image size.
If you do not require translations from the English language, the translation files can be removed to further optimize the size. You can achieve this by specifying the <code>--exclude-files=**java_**.properties</code> option when you run <code>jlink</code>. The default English <code>java.properties</code> file is unaffected.</p>
<h2 id="troubleshooting">Troubleshooting</h2>
<p>The OpenJ9 diagnostic component contains extensive features to assist with problem determination. Diagnostic data is produced under default conditions, but can also be controlled by starting the VM with the <a href="../xdump/">-Xdump option</a> or using the <code>com.ibm.jvm.Dump</code> API. You can also trace Java applications, methods, and VM operations by using the <a href="../xtrace/">-Xtrace option</a>.</p>
<p>To get started, read <a href="../diag_overview/">Diagnostic tools and data</a>.</p>
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