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</li>
</ul>
</nav>
</li>
<li class="md-nav__item">
<a href="../attachapi/" class="md-nav__link">
Java Attach API
</a>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" data-md-toggle="__nav_14" type="checkbox" id="__nav_14" >
<label class="md-nav__link" for="__nav_14">
Diagnostics
<span class="md-nav__icon md-icon"></span>
</label>
<nav class="md-nav" aria-label="Diagnostics" data-md-level="1">
<label class="md-nav__title" for="__nav_14">
<span class="md-nav__icon md-icon"></span>
Diagnostics
</label>
<ul class="md-nav__list" data-md-scrollfix>
<li class="md-nav__item">
<a href="../diag_overview/" class="md-nav__link">
Overview
</a>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" data-md-toggle="__nav_14_2" type="checkbox" id="__nav_14_2" >
<label class="md-nav__link" for="__nav_14_2">
Dumps
<span class="md-nav__icon md-icon"></span>
</label>
<nav class="md-nav" aria-label="Dumps" data-md-level="2">
<label class="md-nav__title" for="__nav_14_2">
<span class="md-nav__icon md-icon"></span>
Dumps
</label>
<ul class="md-nav__list" data-md-scrollfix>
<li class="md-nav__item">
<a href="../dump_javadump/" class="md-nav__link">
Java dump
</a>
</li>
<li class="md-nav__item">
<a href="../dump_heapdump/" class="md-nav__link">
Heap dump
</a>
</li>
<li class="md-nav__item">
<a href="../dump_systemdump/" class="md-nav__link">
System dump
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" data-md-toggle="__nav_14_3" type="checkbox" id="__nav_14_3" >
<label class="md-nav__link" for="__nav_14_3">
Tools
<span class="md-nav__icon md-icon"></span>
</label>
<nav class="md-nav" aria-label="Tools" data-md-level="2">
<label class="md-nav__title" for="__nav_14_3">
<span class="md-nav__icon md-icon"></span>
Tools
</label>
<ul class="md-nav__list" data-md-scrollfix>
<li class="md-nav__item">
<a href="../tool_jextract/" class="md-nav__link">
Dump extractor
</a>
</li>
<li class="md-nav__item">
<a href="../tool_jdmpview/" class="md-nav__link">
Dump viewer
</a>
</li>
<li class="md-nav__item">
<a href="../tool_traceformat/" class="md-nav__link">
Trace formatter
</a>
</li>
<li class="md-nav__item">
<a href="../tool_builder/" class="md-nav__link">
Option builder
</a>
</li>
<li class="md-nav__item">
<a href="../tool_jcmd/" class="md-nav__link">
Java command (jcmd) tool
</a>
</li>
<li class="md-nav__item">
<a href="../tool_jmap/" class="md-nav__link">
Java memory map (jmap) tool
</a>
</li>
<li class="md-nav__item">
<a href="../tool_jps/" class="md-nav__link">
Java process status (jps)
</a>
</li>
<li class="md-nav__item">
<a href="../tool_jstack/" class="md-nav__link">
Java stack (jstack) tool
</a>
</li>
<li class="md-nav__item">
<a href="../tool_jstat/" class="md-nav__link">
Java statistics monitoring (jstat) tool
</a>
</li>
<li class="md-nav__item">
<a href="../tool_migration/" class="md-nav__link">
Switching to OpenJ9
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" data-md-toggle="__nav_14_4" type="checkbox" id="__nav_14_4" >
<label class="md-nav__link" for="__nav_14_4">
Interfaces
<span class="md-nav__icon md-icon"></span>
</label>
<nav class="md-nav" aria-label="Interfaces" data-md-level="2">
<label class="md-nav__title" for="__nav_14_4">
<span class="md-nav__icon md-icon"></span>
Interfaces
</label>
<ul class="md-nav__list" data-md-scrollfix>
<li class="md-nav__item">
<a href="../interface_jvmti/" class="md-nav__link">
JVMTI
</a>
</li>
<li class="md-nav__item">
<a href="../interface_dtfj/" class="md-nav__link">
DTFJ
</a>
</li>
<li class="md-nav__item">
<a href="../interface_lang_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-nav__toggle md-toggle" data-md-toggle="__nav_15" type="checkbox" id="__nav_15" >
<label class="md-nav__link" for="__nav_15">
Command-line options
<span class="md-nav__icon md-icon"></span>
</label>
<nav class="md-nav" aria-label="Command-line options" data-md-level="1">
<label class="md-nav__title" for="__nav_15">
<span class="md-nav__icon md-icon"></span>
Command-line options
</label>
<ul class="md-nav__list" data-md-scrollfix>
<li class="md-nav__item">
<a href="../cmdline_specifying/" class="md-nav__link">
Specifying options
</a>
</li>
<li class="md-nav__item">
<a href="../cmdline_general/" class="md-nav__link">
Standard options
</a>
</li>
<li class="md-nav__item">
<a href="../cmdline_migration/" class="md-nav__link">
Switching to OpenJ9
</a>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" data-md-toggle="__nav_15_4" type="checkbox" id="__nav_15_4" >
<label class="md-nav__link" for="__nav_15_4">
System property options
<span class="md-nav__icon md-icon"></span>
</label>
<nav class="md-nav" aria-label="System property options" data-md-level="2">
<label class="md-nav__title" for="__nav_15_4">
<span class="md-nav__icon md-icon"></span>
System property options
</label>
<ul class="md-nav__list" data-md-scrollfix>
<li class="md-nav__item">
<a href="../d_jvm_commands/" class="md-nav__link">
Using System properties
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmenableclasscaching/" class="md-nav__link">
-Dcom.ibm.enableClassCaching
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmenablelegacydumpsecurity/" class="md-nav__link">
-Dcom.ibm.enableLegacyDumpSecurity
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmenablelegacylogsecurity/" class="md-nav__link">
-Dcom.ibm.enableLegacyLogSecurity
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmenablelegacytracesecurity/" class="md-nav__link">
-Dcom.ibm.enableLegacyTraceSecurity
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmgpudisable/" class="md-nav__link">
-Dcom.ibm.gpu.disable
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmgpuenable/" class="md-nav__link">
-Dcom.ibm.gpu.enable
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmgpuverbose/" class="md-nav__link">
-Dcom.ibm.gpu.verbose
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmlangmanagementosmxbeaniscputime100ns/" class="md-nav__link">
-Dcom.ibm.lang.management.OperatingSystemMXBean.isCpuTime100ns
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmlangmanagementverbose/" class="md-nav__link">
-Dcom.ibm.lang.management.verbose
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmotisharedsharedclassglobalfilterclass/" class="md-nav__link">
-Dcom.ibm.oti.shared.SharedClassGlobalFilterClass
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmtoolsattachcommand_timeout/" class="md-nav__link">
-Dcom.ibm.tools.attach.command_timeout
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmtoolsattachdirectory/" class="md-nav__link">
-Dcom.ibm.tools.attach.directory
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmtoolsattachdisplayname/" class="md-nav__link">
-Dcom.ibm.tools.attach.displayName
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmtoolsattachenable/" class="md-nav__link">
-Dcom.ibm.tools.attach.enable
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmtoolsattachid/" class="md-nav__link">
-Dcom.ibm.tools.attach.id
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmtoolsattachlogging/" class="md-nav__link">
-Dcom.ibm.tools.attach.logging
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmtoolsattachlogname/" class="md-nav__link">
-Dcom.ibm.tools.attach.log.name
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmtoolsattachshutdown_timeout/" class="md-nav__link">
-Dcom.ibm.tools.attach.shutdown_timeout
</a>
</li>
<li class="md-nav__item">
<a href="../dcomibmtoolsattachtimeout/" class="md-nav__link">
-Dcom.ibm.tools.attach.timeout
</a>
</li>
<li class="md-nav__item">
<a href="../dfileencoding/" class="md-nav__link">
-Dfile.encoding
</a>
</li>
<li class="md-nav__item">
<a href="../djavacompiler/" class="md-nav__link">
-Djava.compiler
</a>
</li>
<li class="md-nav__item">
<a href="../djavalangstringsubstringnocopy/" class="md-nav__link">
-Djava.lang.string.substring.nocopy
</a>
</li>
<li class="md-nav__item">
<a href="../djavalangstringbuffergrowaggressively/" class="md-nav__link">
-Djava.lang.stringBuffer.growAggressively
</a>
</li>
<li class="md-nav__item">
<a href="../djdknativecbc/" class="md-nav__link">
-Djdk.nativeCBC
</a>
</li>
<li class="md-nav__item">
<a href="../djdknativechacha20/" class="md-nav__link">
-Djdk.nativeChaCha20
</a>
</li>
<li class="md-nav__item">
<a href="../djdknativecrypto/" class="md-nav__link">
-Djdk.nativeCrypto
</a>
</li>
<li class="md-nav__item">
<a href="../djdknativedigest/" class="md-nav__link">
-Djdk.nativeDigest
</a>
</li>
<li class="md-nav__item">
<a href="../djdknativegcm/" class="md-nav__link">
-Djdk.nativeGCM
</a>
</li>
<li class="md-nav__item">
<a href="../djdknativersa/" class="md-nav__link">
-Djdk.nativeRSA
</a>
</li>
</ul>
</nav>
</li>
<li class="md-nav__item md-nav__item--nested">
<input class="md-nav__toggle md-toggle" data-md-toggle="__nav_15_5" type="checkbox" id="__nav_15_5" >
<label class="md-nav__link" for="__nav_15_5">
JVM -X options
<span class="md-nav__icon md-icon"></span>
</label>
<nav class="md-nav" aria-label="JVM -X options" data-md-level="2">
<label class="md-nav__title" for="__nav_15_5">
<span class="md-nav__icon md-icon"></span>
JVM -X options
</label>
<ul class="md-nav__list" data-md-scrollfix>
<li class="md-nav__item">
<a href="../x_jvm_commands/" class="md-nav__link">
Using -X options
</a>
</li>
<li class="md-nav__item">
<a href="../x/" class="md-nav__link">
-X
</a>
</li>
<li class="md-nav__item">
<a href="../xaggressive/" class="md-nav__link">
-Xaggressive
</a>
</li>
<li class="md-nav__item">
<a href="../xalwaysclassgc/" class="md-nav__link">
-Xalwaysclassgc
</a>
</li>
<li class="md-nav__item">
<a href="../xaot/" class="md-nav__link">
-Xaot
</a>
</li>
<li class="md-nav__item">
<a href="../xargencoding/" class="md-nav__link">
-Xargencoding
</a>
</li>
<li class="md-nav__item">
<a href="../xbootclasspath/" class="md-nav__link">
-Xbootclasspath
</a>
</li>
<li class="md-nav__item">
<a href="../xceehdlr/" class="md-nav__link">
-XCEEHDLR
</a>
</li>
<li class="md-nav__item">
<a href="../xcheck/" class="md-nav__link">
-Xcheck
</a>
</li>
<li class="md-nav__item">
<a href="../xclassgc/" class="md-nav__link">
-Xclassgc
</a>
</li>
<li class="md-nav__item">
<a href="../xcodecache/" class="md-nav__link">
-Xcodecache
</a>
</li>
<li class="md-nav__item">
<a href="../xcodecachetotal/" class="md-nav__link">
-Xcodecachetotal
</a>
</li>
<li class="md-nav__item">
<a href="../xcomp/" class="md-nav__link">
-Xcomp
</a>
</li>
<li class="md-nav__item">
<a href="../xcompactexplicitgc/" class="md-nav__link">
-Xcompactexplicitgc
</a>
</li>
<li class="md-nav__item">
<a href="../xcompactgc/" class="md-nav__link">
-Xcompactgc
</a>
</li>
<li class="md-nav__item">
<a href="../xcompilationthreads/" class="md-nav__link">
-XcompilationThreads
</a>
</li>
<li class="md-nav__item">
<a href="../xcompressedrefs/" class="md-nav__link">
-Xcompressedrefs
</a>
</li>
<li class="md-nav__item">
<a href="../xconcurrentbackground/" class="md-nav__link">
-Xconcurrentbackground
</a>
</li>
<li class="md-nav__item">
<a href="../xconcurrentlevel/" class="md-nav__link">
-Xconcurrentlevel
</a>
</li>
<li class="md-nav__item">
<a href="../xconcurrentslack/" class="md-nav__link">
-Xconcurrentslack
</a>
</li>
<li class="md-nav__item">
<a href="../xconmeter/" class="md-nav__link">
-Xconmeter
</a>
</li>
<li class="md-nav__item">
<a href="../xenableexcessivegc/" class="md-nav__link">
-Xdisableexcessivegc
</a>
</li>
<li class="md-nav__item">
<a href="../xenableexplicitgc/" class="md-nav__link">
-Xdisableexplicitgc
</a>
</li>
<li class="md-nav__item">
<a href="../xdisablejavadump/" class="md-nav__link">
-Xdisablejavadump
</a>
</li>
<li class="md-nav__item">
<a href="../xenablestringconstantgc/" class="md-nav__link">
-Xdisablestringconstantgc
</a>
</li>
<li class="md-nav__item">
<a href="../xdump/" class="md-nav__link">
-Xdump
</a>
</li>
<li class="md-nav__item">
<a href="../xenableexcessivegc/" class="md-nav__link">
-Xenableexcessivegc
</a>
</li>
<li class="md-nav__item">
<a href="../xenableexplicitgc/" class="md-nav__link">
-Xenableexplicitgc
</a>
</li>
<li class="md-nav__item">
<a href="../xenablestringconstantgc/" class="md-nav__link">
-Xenablestringconstantgc
</a>
</li>
<li class="md-nav__item">
<a href="../xfastresolve/" class="md-nav__link">
-Xfastresolve
</a>
</li>
<li class="md-nav__item">
<a href="../xfuture/" class="md-nav__link">
-Xfuture
</a>
</li>
<li class="md-nav__item">
<a href="../xgc/" class="md-nav__link">
-Xgc
</a>
</li>
<li class="md-nav__item">
<a href="../xgcsplitheap/" class="md-nav__link">
-Xgc:splitheap
</a>
</li>
<li class="md-nav__item">
<a href="../xgcmaxthreads/" class="md-nav__link">
-Xgcmaxthreads
</a>
</li>
<li class="md-nav__item">
<a href="../xgcpolicy/" class="md-nav__link">
-Xgcpolicy
</a>
</li>
<li class="md-nav__item">
<a href="../xgcthreads/" class="md-nav__link">
-Xgcthreads
</a>
</li>
<li class="md-nav__item">
<a href="../xgcworkpackets/" class="md-nav__link">
-Xgcworkpackets
</a>
</li>
<li class="md-nav__item">
<a href="../xint/" class="md-nav__link">
-Xint
</a>
</li>
<li class="md-nav__item">
<a href="../xss/" class="md-nav__link">
-Xiss
</a>
</li>
<li class="md-nav__item">
<a href="../xjit/" class="md-nav__link">
-Xjit
</a>
</li>
<li class="md-nav__item">
<a href="../xjni/" class="md-nav__link">
-Xjni
</a>
</li>
<li class="md-nav__item">
<a href="../xlinenumbers/" class="md-nav__link">
-Xlinenumbers
</a>
</li>
<li class="md-nav__item">
<a href="../xloa/" class="md-nav__link">
-Xloa
</a>
</li>
<li class="md-nav__item">
<a href="../xloaminimum/" class="md-nav__link">
-Xloainitial
</a>
</li>
<li class="md-nav__item">
<a href="../xloaminimum/" class="md-nav__link">
-Xloamaximum
</a>
</li>
<li class="md-nav__item">
<a href="../xloaminimum/" class="md-nav__link">
-Xloaminimum
</a>
</li>
<li class="md-nav__item">
<a href="../xlockreservation/" class="md-nav__link">
-XlockReservation
</a>
</li>
<li class="md-nav__item">
<a href="../xlockword/" class="md-nav__link">
-Xlockword
</a>
</li>
<li class="md-nav__item">
<a href="../xlog/" class="md-nav__link">
-Xlog
</a>
</li>
<li class="md-nav__item">
<a href="../xlp/" class="md-nav__link">
-Xlp
</a>
</li>
<li class="md-nav__item">
<a href="../xlpcodecache/" class="md-nav__link">
-Xlp:codecache
</a>
</li>
<li class="md-nav__item">
<a href="../xlpobjectheap/" class="md-nav__link">
-Xlp:objectheap
</a>
</li>
<li class="md-nav__item">
<a href="../xmine/" class="md-nav__link">
-Xmaxe
</a>
</li>
<li class="md-nav__item">
<a href="../xminf/" class="md-nav__link">
-Xmaxf
</a>
</li>
<li class="md-nav__item">
<a href="../xmint/" class="md-nav__link">
-Xmaxt
</a>
</li>
<li class="md-nav__item">
<a href="../xmca/" class="md-nav__link">
-Xmca
</a>
</li>
<li class="md-nav__item">
<a href="../xmca/" class="md-nav__link">
-Xmco
</a>
</li>
<li class="md-nav__item">
<a href="../xmcrs/" class="md-nav__link">
-Xmcrs
</a>
</li>
<li class="md-nav__item">
<a href="../xmine/" class="md-nav__link">
-Xmine
</a>
</li>
<li class="md-nav__item">
<a href="../xminf/" class="md-nav__link">
-Xminf
</a>
</li>
<li class="md-nav__item">
<a href="../xmint/" class="md-nav__link">
-Xmint
</a>
</li>
<li class="md-nav__item">
<a href="../xmn/" class="md-nav__link">
-Xmn
</a>
</li>
<li class="md-nav__item">
<a href="../xmn/" class="md-nav__link">
-Xmns
</a>
</li>
<li class="md-nav__item">
<a href="../xmn/" class="md-nav__link">
-Xmnx
</a>
</li>
<li class="md-nav__item">
<a href="../xmo/" class="md-nav__link">
-Xmo
</a>
</li>
<li class="md-nav__item">
<a href="../xmoi/" class="md-nav__link">
-Xmoi
</a>
</li>
<li class="md-nav__item">
<a href="../xmo/" class="md-nav__link">
-Xmos
</a>
</li>
<li class="md-nav__item">
<a href="../xmo/" class="md-nav__link">
-Xmox
</a>
</li>
<li class="md-nav__item">
<a href="../xmr/" class="md-nav__link">
-Xmr
</a>
</li>
<li class="md-nav__item">
<a href="../xmr/" class="md-nav__link">
-Xmrx
</a>
</li>
<li class="md-nav__item">
<a href="../xms/" class="md-nav__link">
-Xms
</a>
</li>
<li class="md-nav__item">
<a href="../xmso/" class="md-nav__link">
-Xmso
</a>
</li>
<li class="md-nav__item">
<a href="../xms/" class="md-nav__link">
-Xmx
</a>
</li>
<li class="md-nav__item">
<a href="../xaot/" class="md-nav__link">
-Xnoaot
</a>
</li>
<li class="md-nav__item">
<a href="../xclassgc/" class="md-nav__link">
-Xnoclassgc
</a>
</li>
<li class="md-nav__item">
<a href="../xcompactexplicitgc/" class="md-nav__link">
-Xnocompactexplicitgc
</a>
</li>
<li class="md-nav__item">
<a href="../xcompactgc/" class="md-nav__link">
-Xnocompactgc
</a>
</li>
<li class="md-nav__item">
<a href="../xcompressedrefs/" class="md-nav__link">
-Xnocompressedrefs
</a>
</li>
<li class="md-nav__item">
<a href="../xjit/" class="md-nav__link">
-Xnojit
</a>
</li>
<li class="md-nav__item">
<a href="../xlinenumbers/" class="md-nav__link">
-Xnolinenumbers
</a>
</li>
<li class="md-nav__item">
<a href="../xloa/" class="md-nav__link">
-Xnoloa
</a>
</li>
<li class="md-nav__item">
<a href="../xsigcatch/" class="md-nav__link">
-Xnosigcatch
</a>
</li>
<li class="md-nav__item">
<a href="../xsigchain/" class="md-nav__link">
-Xnosigchain
</a>
</li>
<li class="md-nav__item">
<a href="../xnumanone/" class="md-nav__link">
-Xnuma:none
</a>
</li>
<li class="md-nav__item">
<a href="../xoptionsfile/" class="md-nav__link">
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-XX:[+|-]UseGCStartupHints
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-XX:[+|-]UseNoGC
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<!--
* Copyright (c) 2017, 2021 IBM Corp. and others
*
* This program and the accompanying materials are made
* available under the terms of the Eclipse Public License 2.0
* which accompanies this distribution and is available at
* https://www.eclipse.org/legal/epl-2.0/ or the Apache
* License, Version 2.0 which accompanies this distribution and
* is available at https://www.apache.org/licenses/LICENSE-2.0.
*
* This Source Code may also be made available under the
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<h1 id="whats-new-in-version-090">What's new in version 0.9.0</h1>
<p>The following new features and notable changes from v.0.8.0 are included in this release:</p>
<ul>
<li><a href="#binaries-and-supported-platforms">New binaries and supported environments.</a></li>
<li><a href="#idle-tuning-feature">The idle tuning feature is now supported on Linux running on Power&reg; Systems and IBM Z&reg; Systems.</a></li>
<li><a href="#new-gc-policy">A new Garbage Collection (GC) policy is available that performs no housekeeping.</a></li>
<li><a href="#modifying-the-default-java-heap-size-for-applications-that-run-in-containers">A command line option is provided to automatically set a larger Java heap size for applications that run in containers.</a></li>
<li><a href="#specifying-the-maximum-java-heap-size-as-a-percentage-value">You can now specify the maximum Java heap size as a percentage value.</a></li>
<li><a href="#shared-classes-support-for-nested-jar-files">The shared classes feature now supports nested jar files.</a></li>
<li><a href="#direct-dump-reader-enabled-on-linux-and-windows">System dump data can now be read to help diagnose problems on Linux and Windows platforms.</a></li>
<li><a href="#changes-to-the-javalangstring-class">There are notable changes to the <code>java.lang.String</code> class.</a></li>
<li><a href="#changes-to-the-SharedClassCacheInfo-class">There are notable changes to the <code>com.ibm.oti.shared.SharedClassCacheInfo</code> class.</a></li>
</ul>
<h2 id="features-and-changes">Features and changes</h2>
<h3 id="binaries-and-supported-platforms">Binaries and supported platforms</h3>
<p>The following additional OpenJDK binaries that contain the OpenJ9 VM are now available from the AdoptOpenJDK community:</p>
<ul>
<li><a href="https://adoptopenjdk.net/?variant=openjdk10-openj9">OpenJDK version 10</a></li>
<li><a href="https://adoptopenjdk.net/releases.html?variant=openjdk8-openj9#x32_win">OpenJDK version 8 for 32-bit Windows</a></li>
<li><a href="https://adoptopenjdk.net/nightly.html?variant=openjdk8-openj9">OpenJDK version 8 for x86 64-bit Linux (Large Heap)</a> for Java heaps &gt;57 GB.</li>
</ul>
<p>Complete platform support information for OpenJ9 can be found in <a href="#openj9_support.md">Supported environments</a></p>
<h3 id="idle-tuning-feature">Idle tuning feature</h3>
<p>The idle tuning feature in OpenJ9 keeps your memory footprint small by releasing unused memory back to the
operating system. Prior to Eclipse v 0.9.0 this feature was available only on Linux x86 architectures with the
<code>gencon</code> garbage collection policy. From v 0.9.0, this feature is now available on Linux for IBM POWER&reg; and IBM Z&reg; architectures.
For more information about this feature, see the following command line options, which control this
behavior:</p>
<ul>
<li><a href="../xxidletuningcompactonidle/">-XX:[+|-]IdleTuningCompactOnIdle</a></li>
<li><a href="../xxidletuninggconidle/">-XX:[+|-]IdleTuningGcOnIdle</a></li>
<li><a href="../xxidletuningminidlewaittime/">-XX:IdleTuningMinIdleWaitTime</a></li>
<li><a href="../xxidletuningminfreeheaponidle/">-XX:IdleTuningMinFreeHeapOnIdle</a></li>
</ul>
<p>The following blog post describes the benefits of using this feature: <a href="https://developer.ibm.com/javasdk/2017/09/25/still-paying-unused-memory-java-app-idle/">Are you still paying for unused memory when your Java app is idle?</a></p>
<h3 id="new-gc-policy">New GC policy</h3>
<p>A new GC policy is introduced for <a href="http://openjdk.java.net/jeps/318">JEP 318: Epsilon: A No-Op Garbage Collector</a>.</p>
<p>When this policy is enabled, the Java object heap is expanded in the normal way until the limit is
reached, but memory is not reclaimed through garbage collection. When the limit is reached the VM shuts down.</p>
<p>This JEP has a number of use cases including short-lived applications and certain test scenarios.</p>
<p>To enable this policy you can use one of the following options:</p>
<ul>
<li><a href="../xgcpolicy/">-Xgcpolicy:nogc</a></li>
<li><a href="../xxusenogc/">-XX:+UseNoGC</a></li>
</ul>
<h3 id="modifying-the-default-java-heap-size-for-applications-that-run-in-containers">Modifying the default Java heap size for applications that run in containers</h3>
<p>When using container technology, applications are typically run on their own and do not need to compete for memory. In this release, changes
are introduced to detect when OpenJ9 is running inside a container. If your application is running in a container and
you want the VM to allocate a larger fraction of memory to the Java heap, set the <a href="../xxusecontainersupport/"><code>-XX:+UseContainerSupport</code></a> option on the command line.</p>
<p>The following table shows the maximum Java heap size that gets set, depending on the memory available:</p>
<table>
<thead>
<tr>
<th>Physical memory <code>&lt;size&gt;</code></th>
<th>Maximum Java heap size</th>
</tr>
</thead>
<tbody>
<tr>
<td>Less than 1 GB</td>
<td>50% <code>&lt;size&gt;</code></td>
</tr>
<tr>
<td>1 GB - 2 GB</td>
<td><code>&lt;size&gt;</code> - 512M</td>
</tr>
<tr>
<td>Greater than 2 GB</td>
<td>75% <code>&lt;size&gt;</code></td>
</tr>
</tbody>
</table>
<p>The default heap size for containers only takes affect when running in a container environment and when <code>-XX:+UseContainerSupport</code> is specified,
which is expected to be the default in a future release.</p>
<h3 id="specifying-the-maximum-java-heap-size-as-a-percentage-value">Specifying the maximum Java heap size as a percentage value</h3>
<p>OpenJ9 now supports setting the heap size as a percentage of the physical memory. The following OpenJDK options are recognized and can be
set for the VM:</p>
<ul>
<li><code>-XX:MaxRAMPercentage</code></li>
<li><code>-XX:InitialRAMPercentage</code></li>
</ul>
<p>To understand how to set these options, see <a href="../xxinitialrampercentage/">-XX:InitialRAMPercentage / -XX:MaxRAMPercentage</a>.</p>
<p>If your application is running in a container and you have specified <code>-XX:+UseContainerSupport</code>, as described in <a href="#modifying-the-default-java-heap-size-for-applications-that-run-in-containers">Modifying the default Java heap size for applications that run in containers</a>, both the default heap size for containers and the <code>-XX:MaxRAMPercentage</code> and <code>-XX:InitialRAMPercentage</code>
options are based on the available container memory.</p>
<h3 id="shared-classes-support-for-nested-jar-files">Shared classes support for nested jar files</h3>
<p>Changes are made to the <code>com.ibm.oti.shared</code> API to support nested jar files.</p>
<h3 id="direct-dump-reader-enabled-on-linux-and-windows">Direct Dump Reader enabled on Linux and Windows</h3>
<p>Direct Dump Reader (DDR) support is now enabled for the OpenJ9 VM on all Linux architectures and on Windows. The DDR code enables the VM to read system dump data by using the OpenJ9 Diagnostic Tool
Framework for Java (DTFJ) API or the <a href="../tool_jdmpview/"><code>jdmpview</code></a> tool. If you use the <a href="https://www.eclipse.org/mat/">Eclipse Memory Analyzer Tool (MAT)</a>, you can also analyze OpenJ9 or IBM VMs by installing the DTFJ plugin.
(Install from the Eclipse Help menu; Install New Software &gt; Work with "IBM Diagnostic Tool Framework for Java" &gt; IBM Monitoring and Diagnostic Tools &gt; Diagnostic Tool Framework for Java)</p>
<p>You must use a 32-bit VM to look at a 32-bit core, and a 64-bit VM to look at a 64-bit core. This restriction will be fixed in a later version of OpenJ9.</p>
<h3 id="changes-to-the-javalangstring-class">Changes to the <code>java.lang.String</code> class</h3>
<p><img alt="Start of content that applies only to Java 9 and later" src="../cr/java9plus.png" /> To match the behavior of OpenJDK, <code>java.lang.String</code> no longer has a count field, which changes the way that <code>String.subString()</code> works compared to Java 8. <code>String.subString()</code> now copies the value array. Similarly, <code>StringBuffer</code> and <code>StringBuilder</code> do not share the value array with any <code>String</code> created by <code>toString()</code>.</p>
<p>For performance and compatibility with the new String object layout, the OpenJ9 implementations of <code>StringBuffer</code> and <code>StringBuilder</code> have been deprecated in favor of the OpenJDK implementations.
<img alt="End of content that applies only to Java 9 or later" src="../cr/java_close.png" /></p>
<h3 id="changes-to-the-sharedclasscacheinfo-class">Changes to the <code>SharedClassCacheInfo</code> class</h3>
<p><img alt="Start of content that applies only to Java 10 and later" src="../cr/java10plus.png" /> <code>SharedClassCacheInfo.getCacheJVMLevel()</code> used to return the JVMLEVEL constant that maps to a Java version number, for example <strong>JVMLEVEL_JAVA8</strong>. This call now returns only the Java version number, for example <strong>10</strong> for Java 10.
<img alt="End of content that applies only to Java 10 or later" src="../cr/java_close.png" /></p>
<h2 id="full-release-information">Full release information</h2>
<p>To see a complete list of changes between Eclipse OpenJ9 v 0.8.0 and v 0.9.0 releases, see the <a href="https://github.com/eclipse-openj9/openj9/blob/master/doc/release-notes/0.9/0.9.md">Release notes</a>.</p>
<!-- ==== END OF TOPIC ==== cmdline_general.md ==== -->
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