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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii" /><meta http-equiv="Content-Type" content="text/html; charset=us-ascii" /><title>JEP 248: Make G1 the Default Garbage Collector</title><link rel="shortcut icon" href="/images/nanoduke.ico" /><link rel="stylesheet" type="text/css" href="/page.css" /><script type="text/javascript" src="/page.js"><noscript></noscript></script><script src="https://cdn.usefathom.com/script.js" data-site="KCYJJPZX" defer="yes"></script><style type="text/css" xml:space="preserve"> TABLE { border-collapse: collapse; padding: 0px; margin: 1em 0 1em 2em; } TR:first-child TH, TR:first-child TD { padding-top: 0; } TH, TD { padding: 0px; padding-top: .5ex; vertical-align: baseline; text-align: left; } TD + TD, TH + TH { padding-left: 1em; } TD:first-child, TH:first-child, TD.jep { text-align: right; } TABLE.head TD:first-child { font-style: italic; padding-left: 2em; white-space: nowrap; } PRE { padding-left: 2em; margin: 1ex 0; font-size: inherit; } TABLE PRE { padding-left: 0; margin: 0; } TABLE.jeps TD:first-child + TD, TABLE.jeps TD:first-child + TD + TD { padding-left: .5em; } TABLE.jeps TD:first-child, TABLE.jeps TD:first-child + TD, TABLE.jeps TD:first-child + TD + TD { font-size: smaller; } TABLE.jeps TD.cl { font-size: smaller; padding-right: 0; text-align: right; } TABLE.jeps TD.cm { font-size: smaller; padding-left: .1em; padding-right: .1em; } TABLE.jeps TD.cr { font-size: smaller; padding-left: 0; } TABLE.jeps TD.z { padding-left: 0; padding-right: 0; } TABLE.head TD { padding-top: 0; } </style></head><body><div id="main"><h1>JEP 248: Make G1 the Default Garbage Collector</h1><table class="head"><tr><td>Owner</td><td>Stefan Johansson</td></tr><tr><td>Type</td><td>Feature</td></tr><tr><td>Scope</td><td>JDK</td></tr><tr><td>Status</td><td>Closed / Delivered</td></tr><tr><td>Release</td><td>9</td></tr><tr><td>Component</td><td>hotspot / gc</td></tr><tr><td>Discussion</td><td>hotspot dash dev at openjdk dot java dot net</td></tr><tr><td>Effort</td><td>M</td></tr><tr><td>Duration</td><td>M</td></tr><tr><td>Reviewed by</td><td>Mikael Vidstedt</td></tr><tr><td>Endorsed by</td><td>Mikael Vidstedt</td></tr><tr><td>Created</td><td>2015/02/16 19:58</td></tr><tr><td>Updated</td><td>2017/09/12 14:30</td></tr><tr><td>Issue</td><td><a href="https://bugs.openjdk.org/browse/JDK-8073273">8073273</a></td></tr></table><div class="markdown"><h2 id="Summary">Summary</h2> <p>Make G1 the default garbage collector on 32- and 64-bit server configurations.</p> <h2 id="Motivation">Motivation</h2> <p>Limiting GC pause times is, in general, more important than maximizing throughput. Switching to a low-pause collector such as G1 should provide a better overall experience, for most users, than a throughput-oriented collector such as the Parallel GC, which is currently the default.</p> <p>Many performance improvements were made to G1 in JDK 8 and its update releases, and further improvements are planned for JDK 9. The introduction of concurrent class unloading (<a href="http://openjdk.java.net/jeps/156">JEP 156</a>) in JDK 8u40 made G1 a fully-featured garbage collector, ready to be the default.</p> <h2 id="Description">Description</h2> <p>Changing the default collector is straightforward.</p> <h2 id="Risks-and-Assumptions">Risks and Assumptions</h2> <ul> <li> <p>The change is based on the assumption that limiting latency is often more important than maximizing throughput. If this assumption is incorrect then this change might need to be reconsidered.</p> </li> <li> <p>G1 is seen as a robust and well-tested collector. It is not expected to have stability problems, but becoming the default collector will increase its visibility and may reveal previously-unknown issues. If a critical issue is found that can't be addressed in the JDK 9 time frame, we will revert back to use Parallel GC as the default for the JDK 9 GA.</p> </li> <li> <p>The resource usage of G1 is different from Parallel. When resource usage overhead needs to be minimized a collector other than G1 should be used, and after this change the alternate collector will have to be specified explicitly.</p> </li> </ul> </div></div><div id="sidebar"><div id="openjdk-sidebar-logo"><a href="/"><img alt="OpenJDK logo" width="91" height="25" src="/images/openjdk2.svg" /></a></div><div class="links"><div class="link"><a href="/install/">Installing</a></div><div class="link"><a href="/guide/#contributing-to-an-openjdk-project">Contributing</a></div><div class="link"><a href="/guide/#reviewing-and-sponsoring-a-change">Sponsoring</a></div><div class="link"><a href="/guide/">Developers' Guide</a></div><div class="link"><a href="/groups/vulnerability/report">Vulnerabilities</a></div><div class="link"><a href="https://jdk.java.net">JDK GA/EA Builds</a></div></div><div class="links"><div class="links"><a href="https://mail.openjdk.org">Mailing lists</a></div><div class="link"><a href="https://wiki.openjdk.org">Wiki</a> · <a 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