{"id":2056,"date":"2020-01-03T08:08:12","date_gmt":"2020-01-03T00:08:12","guid":{"rendered":"https:\/\/coderbee.net\/?p=2056"},"modified":"2020-01-02T21:30:23","modified_gmt":"2020-01-02T13:30:23","slug":"cms-gc","status":"publish","type":"post","link":"https:\/\/coderbee.net\/index.php\/jvm\/20200103\/2056","title":{"rendered":"CMS GC"},"content":{"rendered":"<h1>1. \u6982\u8ff0<\/h1>\n<p>CMS\uff0cMost concurrently\uff0c\u662f\u4e00\u6b3e \u91c7\u7528 \u5e76\u53d1-\u6807\u8bb0-\u6e05\u9664\uff08Concurrent-Mark-Sweep\uff09\u7b97\u6cd5\u3001\u9488\u5bf9\u8001\u5e74\u4ee3\u7684 GC\uff0c\u5176\u76ee\u7684\u662f\u6700\u5c0f\u5316\u6682\u505c\u65f6\u95f4\u3002<\/p>\n<p>CMS GC \u5728 JDK 9 \u88ab\u6807\u8bb0\u4e3a deprecated\u3002<\/p>\n<h1>2. \u6267\u884c\u8fc7\u7a0b<\/h1>\n<p>CMS \u7684\u6807\u8bb0\u8fc7\u7a0b\u91c7\u7528\u6307\u9488\u53ef\u8fbe\u6027\u5206\u6790\u65b9\u6cd5\uff0c\u5bf9\u4e8e\u5b58\u6d3b\u7684\u5bf9\u8c61\uff0c\u5728\u5bf9\u8c61\u5934\u4e0a\u8fdb\u884c\u6807\u8bb0\u3002<\/p>\n<h2>2.1 \u521d\u59cb\u6807\u8bb0<\/h2>\n<p>\u4ece GC Roots\u3001\u65b0\u751f\u4ee3\uff08Eden\u3001From\u3001To\uff09\u51fa\u53d1\u6807\u8bb0\u76f4\u63a5\u5173\u8054\u7684\u5bf9\u8c61\u3002<\/p>\n<p><strong>\u9700\u8981 STW \u3002<\/strong><\/p>\n<h2>2.2 \u5e76\u53d1\u6807\u8bb0<\/h2>\n<p>\u8be5\u9636\u6bb5\u8fdb\u884c GC Root Tracing\uff0c\u4ece\u521d\u59cb\u6807\u8bb0\u9636\u6bb5 \u6807\u8bb0\u8fc7\u7684\u5bf9\u8c61\u51fa\u53d1\uff0c\u6807\u8bb0\u6240\u6709\u53ef\u8fbe\u7684\u5bf9\u8c61\u3002<\/p>\n<p>\u4e0e\u5e94\u7528\u7ebf\u7a0b\u5e76\u53d1\u6267\u884c\uff0c\u53ef\u4ee5\u91c7\u7528\u591a\u4e2a\u6807\u8bb0\u7ebf\u7a0b\u8fdb\u884c\u5e76\u53d1\u6807\u8bb0\u3002<\/p>\n<h2>2.3 \u9884\u6e05\u7406<\/h2>\n<p>\u6b64\u9636\u6bb5\u4ece\u65b0\u751f\u4ee3\u664b\u5347\u7684\u5bf9\u8c61\u3001\u65b0\u5206\u914d\u5230\u8001\u5e74\u4ee3\u7684\u5bf9\u8c61\u4ee5\u53ca\u5728\u5e76\u53d1\u9636\u6bb5\u4fee\u6539\u4e86\u7684\u5bf9\u8c61 \u51fa\u53d1\u8fdb\u884c\u6807\u8bb0\u3002<br \/>\n\u5728\u5e76\u53d1\u6807\u8bb0\u9636\u6bb5\uff0c\u5982\u679c\u8001\u5e74\u4ee3\u4e2d\u6709\u5bf9\u8c61\u5185\u90e8\u5f15\u7528\u53d1\u751f\u53d8\u5316\uff0c\u4f1a\u628a\u6240\u5728\u7684 card \u6807\u8bb0\u4e3a dirty\uff0c\u901a\u8fc7\u626b\u63cf\u8fd9\u4e9b card\uff0c\u91cd\u65b0\u6807\u8bb0\u90a3\u4e9b\u5728\u5e76\u53d1\u9636\u6bb5\u5f15\u7528\u88ab\u66f4\u65b0\u7684\u5bf9\u8c61\u3002<\/p>\n<p>\u901a\u8fc7 -XX:-CMSPrecleaningEnabled \u53c2\u6570\u9009\u62e9\u5173\u95ed\u8be5\u9636\u6bb5\uff0c\u9ed8\u8ba4\u5f00\u542f\u3002<\/p>\n<p>\u76ee\u7684\u662f\u51cf\u5c11\u91cd\u65b0\u6807\u8bb0\u9636\u6bb5\u7684\u6682\u505c\u65f6\u95f4\u3002<\/p>\n<p>CMS \u63d0\u4f9b\u4e86\u53c2\u6570 CMSScavengeBeforeRemark \u5728 \u91cd\u65b0\u6807\u8bb0\u4e4b\u524d\u5f3a\u5236\u8fdb\u884c\u4e00\u6b21 minor GC\uff0c\u8fd9\u6837\u505a\u7684\u597d\u5904\u662f\u7f29\u77ed\u4e86\u91cd\u65b0\u6807\u8bb0\u9636\u6bb5\u7684\u6682\u505c\u65f6\u95f4\uff0c\u574f\u5904\u662f Minor GC \u540e\u7d27\u8ddf\u7740\u4e00\u4e2a \u91cd\u65b0\u6807\u8bb0\u7684 \u6682\u505c\uff0c\u8fd9\u6837\u4f7f\u505c\u987f\u65f6\u95f4\u4e5f\u6bd4\u8f83\u4e45\u3002<\/p>\n<p><!--more--><\/p>\n<h2>2.4 \u53ef\u4e2d\u65ad\u9884\u6e05\u7406<\/h2>\n<p>\u8be5\u9636\u6bb5\u5b58\u5728\u7684\u76ee\u7684\u662f\u51cf\u5c11\u91cd\u65b0\u6807\u8bb0\u7684\u5de5\u4f5c\u91cf\uff0c\u51cf\u5c11\u6682\u505c\u65f6\u95f4\u3002\u4e3b\u8981\u505a\u4e24\u4ef6\u4e8b\uff1a<\/p>\n<ul>\n<li>\n<ol>\n<li>\u626b\u63cf dirty card \u4e2d\u7684\u5bf9\u8c61\uff1b<\/li>\n<\/ol>\n<\/li>\n<li>\n<ol>\n<li>\u5904\u7406\u65b0\u751f\u4ee3\u5f15\u7528\u5230\u8001\u5e74\u4ee3\u7684\u5bf9\u8c61\u3002<\/li>\n<\/ol>\n<\/li>\n<\/ul>\n<p>\u5728\u9884\u6e05\u7406\u6b65\u9aa4\u540e\uff0c\u5982\u679c\u6ee1\u8db3\u4e0b\u9762\u4e24\u4e2a\u6761\u4ef6\uff0c\u5c31\u4e0d\u4f1a\u5f00\u542f\u53ef\u4e2d\u65ad\u7684\u9884\u6e05\u7406\uff0c\u76f4\u63a5\u8fdb\u5165\u91cd\u65b0\u6807\u8bb0\u9636\u6bb5\uff1a<\/p>\n<ul>\n<li>Eden\u7684\u4f7f\u7528\u7a7a\u95f4\u5927\u4e8e\u201cCMSScheduleRemarkEdenSizeThreshold\u201d\uff0c\u8fd9\u4e2a\u53c2\u6570\u7684\u9ed8\u8ba4\u503c\u662f2M\uff1b<\/li>\n<li>Eden\u7684\u4f7f\u7528\u7387\u5927\u4e8e\u7b49\u4e8e\u201cCMSScheduleRemarkEdenPenetration\u201d\uff0c\u8fd9\u4e2a\u53c2\u6570\u7684\u9ed8\u8ba4\u503c\u662f50%\u3002<\/li>\n<\/ul>\n<p>\u8be5\u9636\u6bb5\u9000\u51fa\u7684\u6761\u4ef6\u6709\u4e09\u4e2a\uff1a<\/p>\n<ol>\n<li><code>-XX:CMSAbortablePrecleanTime=n<\/code> \u53c2\u6570\u63a7\u5236\uff0c\u9ed8\u8ba45\u79d2\u9000\u51fa\uff1b\u8be5\u9636\u6bb5\u6301\u7eed\u7684\u65f6\u95f4\u8d85\u8fc7 n \u79d2\u3002<\/li>\n<li>Eden \u533a\u8fbe\u5230 <code>-XX:CMScheduleRemarkEdenPenetration=n<\/code> \u53c2\u6570\u914d\u7f6e\u7684\u503c\uff08\u9ed8\u8ba4 50%\uff09\uff1beden \u7684\u4f7f\u7528\u7387\u8d85\u8fc7\u67d0\u4e2a\u9608\u503c\u3002<\/li>\n<li><code>-XX:CMSMaxAbortablePrecleanLoops=n<\/code> \u63a7\u5236\u7684\u626b\u63cf\u6b21\u6570\uff08\u9ed8\u8ba4\u662f0\u8868\u793a\u9650\u5236\u6b21\u6570\uff09\u3002\u5faa\u73af\u6b21\u6570\u9650\u5236\u3002<\/li>\n<\/ol>\n<p>\u8be5\u9636\u6bb5\u662f\u5e0c\u671b\u53d1\u751f\u4e00\u6b21 Minor GC\uff0c\u8fd9\u6837\u5c31\u53ef\u4ee5\u51cf\u5c11 Eden \u533a\u5bf9\u8c61\u7684\u6570\u91cf\uff0c\u964d\u4f4e\u91cd\u65b0\u6807\u8bb0\u7684\u5de5\u4f5c\u91cf\uff0c\u56e0\u4e3a\u91cd\u65b0\u6807\u8bb0\u9700\u8981\u626b\u63cf\u6574\u4e2a Eden\uff08\u4e0d\u626b\u63cf from\u3001to \u662f\u56e0\u4e3a\u65b0\u5bf9\u8c61\u4e0d\u4f1a\u5206\u914d\u5728\u8fd9\u91cc\uff0c\u521d\u59cb\u6807\u8bb0\u9636\u6bb5\u626b\u63cf\u4e00\u6b21\u5c31\u591f\u4e86\uff09\u3002<\/p>\n<h2>2.5 \u91cd\u65b0\u6807\u8bb0<\/h2>\n<p>\u4e3b\u8981\u904d\u5386\u4e09\u4e2a\u5730\u65b9\u8fdb\u884c\u91cd\u65b0\u6807\u8bb0\uff1a<\/p>\n<ol>\n<li>Eden\u533a\uff08To survivor \u5e94\u8be5\u4e5f\u8981\uff1f\uff09<\/li>\n<li>Dirty card<\/li>\n<li>GC Roots<\/li>\n<\/ol>\n<p><strong>\u6b64\u9636\u6bb5\u662f STW \u7684\u3002<\/strong><\/p>\n<p>\u5728\u91cd\u65b0\u6807\u8bb0\u9636\u6bb5\uff0c\u5982\u679c\u65b0\u751f\u4ee3\u6709\u5f88\u591a\u5b58\u6d3b\u7684\u5bf9\u8c61\uff0c\u5c31\u4f1a\u5bfc\u81f4 STW \u5f88\u957f\uff0cCMS \u63d0\u4f9b\u53c2\u6570 <code>-XX:+CMSScavengeBeforeRemark<\/code> \u6765\u5f3a\u5236\u5728\u8fdb\u5165\u6b64\u9636\u6bb5\u524d\u8fdb\u884c minor gc \u3002<\/p>\n<h2>2.6 \u5e76\u53d1\u6e05\u7406<\/h2>\n<p>\u5e76\u53d1\u626b\u63cf\u5806\u4e2d\u7684\u6bcf\u4e00\u4e2a\u5bf9\u8c61\uff0c\u6e05\u7406\u672a\u6807\u8bb0\u7684\u5bf9\u8c61\uff08\u5783\u573e\uff09\uff0c\u5bf9\u4e8e\u5df2\u6807\u8bb0\u7684\u5bf9\u8c61\u6e05\u7406\u5176\u6807\u8bb0\u4f4d\uff0c\u4ee5\u4fbf\u4e0b\u6b21\u56de\u6536\u626b\u63cf\u3002<\/p>\n<h2>2.7 \u5e76\u53d1\u91cd\u7f6e<\/h2>\n<p>\u91cd\u7f6e CMS\u5185\u90e8\u7684\u6570\u636e\u7ed3\u6784\u3002<\/p>\n<h1>3. \u5f02\u5e38\u60c5\u51b5<\/h1>\n<h2>3.1 \u5e76\u53d1\u6a21\u5f0f\u5931\u8d25<\/h2>\n<p>\u65b0\u751f\u4ee3\u53d1\u751f\u5783\u573e\u56de\u6536\uff0c\u540c\u4e8b\u8001\u5e74\u4ee3\u6709\u6ca1\u6709\u8db3\u591f\u7684\u7a7a\u95f4\u5bb9\u7eb3\u664b\u5347\u7684\u5bf9\u8c61\u65f6\uff0c\u5c31\u53d1\u751f\u4e86 concurrent mode failure\uff0cCMS \u5783\u573e\u56de\u6536\u5c31\u4f1a\u9000\u5316\u6210 Full GC\uff0c\u8fd9\u4e2a\u56de\u6536\u8fc7\u7a0b\u662f\u5355\u7ebf\u7a0b\u7684\u3002<\/p>\n<p>\u53d1\u751f\u5e76\u53d1\u6a21\u5f0f\u5931\u6548\u5f80\u5f80\u662f\u7531\u4e8e CMS \u4e0d\u80fd\u4ee5\u8db3\u591f\u5feb\u7684\u901f\u5ea6\u6e05\u7406\u8001\u5e74\u4ee3\u7a7a\u95f4\uff1a\u65b0\u751f\u4ee3\u9700\u8981\u8fdb\u884c\u5783\u573e\u56de\u6536\u65f6\uff0cCMS \u6536\u96c6\u5668\u8ba1\u7b97\u53d1\u73b0\u8001\u5e74\u4ee3\u6ca1\u6709\u8db3\u591f\u7684\u7a7a\u95f2\u7a7a\u95f4\u53ef\u4ee5\u5bb9\u7eb3\u8fd9\u4e9b\u664b\u5347\u5bf9\u8c61\uff0c\u4e0d\u5f97\u4e0d\u5148\u5bf9\u8001\u5e74\u4ee3\u8fdb\u884c\u5783\u573e\u56de\u6536\u3002<\/p>\n<p>\u5e76\u53d1\u6a21\u5f0f\u5e76\u4e0d\u5fc5\u987b\u5bfc\u81f4 Full GC\uff0c\u5728\u7279\u5b9a\u7684\u60c5\u51b5\u4e0b\uff0cJVM \u5c06\u53ea\u662f\u7b49\u5f85\u5e76\u53d1\u6536\u96c6\u5468\u671f\u7ed3\u675f\uff0c\u4f46\u5e94\u7528\u7a0b\u5e8f\u5c06\u5904\u4e8e STW \u72b6\u6001\u76f4\u81f3 YGC \u7ed3\u675f\u3002<\/p>\n<p>\u5e76\u53d1\u6a21\u5f0f\u5931\u8d25\u901a\u5e38\u662f\u7531\u4e8e CMS \u5468\u671f\u5f00\u59cb\u5f97\u592a\u665a\u3002<\/p>\n<h2>3.2 \u664b\u5347\u5931\u8d25<\/h2>\n<p>\u65b0\u751f\u4ee3\u505a minor gc \u65f6\uff0c\u9700\u8981 CMS \u7684\u62c5\u4fdd\u673a\u5236\u786e\u8ba4\u8001\u5e74\u4ee3\u662f\u5426\u6709\u8db3\u591f\u7684\u7a7a\u95f4\u5bb9\u7eb3\u664b\u5347\u7684\u5bf9\u8c61\uff1b\u5982\u679c\u62c5\u4fdd\u673a\u5236\u53d1\u73b0\u4e0d\u591f\uff0c\u5219\u62a5 concurrent mode failure\uff1b\u5982\u679c\u62c5\u4fdd\u673a\u5236\u5224\u65ad\u662f\u591f\u7684\uff0c\u4f46\u5b9e\u9645\u7531\u4e8e\u788e\u7247\u95ee\u9898\u5bfc\u81f4\u65e0\u6cd5\u5206\u914d\uff0c\u5219\u62a5\u664b\u5347\u5931\u8d25\u3002<\/p>\n<p>\u51fa\u73b0\u664b\u5347\u5931\u8d25\u65f6\uff0cCMS \u6536\u96c6\u5668\u5728\u65b0\u751f\u4ee3\u5783\u573e\u6536\u96c6\u8fc7\u7a0b\u4e2d\uff08STW\uff09\uff0c\u5bf9\u6574\u4e2a\u8001\u5e74\u4ee3\u7a7a\u95f4\u8fdb\u884c\u4e86\u6574\u7406\u548c\u538b\u7f29\u3002\u7531\u4e8e\u9700\u8981\u5bf9\u6574\u4e2a\u5806\u8fdb\u884c\u6574\u7406\uff0c\u6682\u505c\u65f6\u95f4\u6bd4\u5e76\u53d1\u6a21\u5f0f\u5931\u8d25\u8981\u957f\u5f88\u591a\u3002<\/p>\n<h2>3.3 \u6c38\u4e45\u4ee3\u8017\u5c3d<\/h2>\n<p>\u9ed8\u8ba4\u60c5\u51b5\u4e0b\uff0cCMS \u4e0d\u4f1a\u5bf9\u6c38\u4e45\u4ee3\u8fdb\u884c\u6536\u96c6\uff0c\u4e00\u65e6\u6c38\u4e45\u4ee3\u7a7a\u95f4\u8017\u5c3d\uff0c\u89e6\u53d1 Full GC\u3002<\/p>\n<h1>4.  CMS GC \u7684\u89e6\u53d1\u6761\u4ef6<\/h1>\n<ol>\n<li>\n<p>\u5468\u671f\u6027\u89e6\u53d1\uff1a\u540e\u53f0\u7ebf\u7a0b &#8220;ConcurrentMarkSweepThread&#8221; \u5faa\u73af\uff08\u9ed8\u8ba4\u95f4\u96942\u79d2\uff09\u5224\u65ad\u662f\u5426\u9700\u8981\u89e6\u53d1\uff0c\u901a\u8fc7\u8bbe\u7f6e <code>-XX:-UseCMSInitiatingOccupancyOnly<\/code> \u6765\u7981\u6b62\u8fd9\u4e2a\u81ea\u884c\u5224\u65ad\u3002<\/p>\n<\/li>\n<li>\n<p>\u8001\u5e74\u4ee3\u4f7f\u7528\u7387\u8fbe\u5230\u9608\u503c <code>CMSInitiatingOccupancyFraction<\/code>\uff0c\u9ed8\u8ba4 92%<\/p>\n<\/li>\n<\/ol>\n<h1>5. Full GC<\/h1>\n<p>Full GC \u662f\u5728 STW \u4e0b\u8fdb\u884c\u3002<\/p>\n<p>Full GC \u5e76\u4e0d\u603b\u662f\u8fdb\u884c\u538b\u7f29\uff0c\u901a\u8fc7\u53c2\u6570 <code>-XX:CMSFullGCsBeforeCompaction=&lt;N&gt;<\/code> \u8bbe\u7f6e\u7ecf\u8fc7 N \u6b21\u4e0d\u538b\u7f29\u7684 Full GC \u540e\u6267\u884c\u4e00\u6b21\u5e26\u538b\u7f29\u7684 Full GC\u3002<br \/>\n<code>-XX:+UseCMSCompactAtFullCollection<\/code>\uff0c\u9ed8\u8ba4\u4e3a true\uff0c\u5728\u8fdb\u884c Full GC \u65f6\u8fdb\u884c\u5185\u5b58\u6574\u7406\u3002<\/p>\n<h2>5.1 \u89e6\u53d1\u6761\u4ef6<\/h2>\n<ol>\n<li>\u663e\u5f0f\u8c03\u7528 <code>System.gc()<\/code> \u3001\u4e14\u6ca1\u6709\u5f00\u542f\u53c2\u6570 <code>-XX:+ExplicitGCInvokesConcurrent<\/code> \uff1b<\/li>\n<li>\u901a\u8fc7\u5de5\u5177 <code>jmap -histo:live &lt;pid&gt;<\/code> \u663e\u5f0f\u89e6\u53d1\uff1b<\/li>\n<li>\u664b\u5347\u5931\u8d25\u6216\u5e76\u53d1\u6a21\u5f0f\u5931\u8d25\uff1b<\/li>\n<li>\u7edf\u8ba1\u5f97\u5230\u7684 Minor GC \u664b\u5347\u5230\u8001\u5e74\u4ee3\u7684\u5e73\u5747\u5927\u5c0f\u5927\u4e8e\u8001\u5e74\u4ee3\u7684\u5269\u4f59\u7a7a\u95f4\uff1b<\/li>\n<li>\u8001\u5e74\u4ee3\u6216\u6c38\u4e45\u4ee3 OOM \u3002<\/li>\n<li>\u5143\u7a7a\u95f4\u8fbe\u5230 MaxMetaspaceSize \u3002<\/li>\n<\/ol>\n<h1>6. \u4e3a\u4ec0\u4e48\u4e0d\u63a8\u8350 CMS GC<\/h1>\n<p>\u6765\u81ea <a href=\"http:\/\/hellojava.info\/?p=142\">http:\/\/hellojava.info\/?p=142<\/a><\/p>\n<ol>\n<li>\u89e6\u53d1\u6bd4\u4f8b\u4e0d\u597d\u8bbe\u7f6e\u3002<\/li>\n<li>\u62a2\u5360 CPU\u3002<\/li>\n<li>YGC \u901f\u5ea6\u53d8\u6162\u3002\u664b\u5347\u65f6\u9700\u8981\u67e5\u627e\u7a7a\u95f2\u7a7a\u95f4\u3002<\/li>\n<li>\u788e\u7247\u95ee\u9898\u5e26\u6765\u4e25\u91cd\u540e\u679c\u3002<\/li>\n<\/ol>\n<p>CMS GC \u670970 \u591a\u4e2a\u53c2\u6570\u53ef\u8bbe\u7f6e\uff0c\u8c03\u4f18\u590d\u6742\u3002<\/p>\n<h1>7. \u76f8\u5173\u53c2\u6570<\/h1>\n<p>\u542f\u7528 CMS GC\uff1a <code>-XX:+UseConcMarkSweepGC<\/code> \uff0c\u9ed8\u8ba4\u642d\u914d\u7684\u65b0\u751f\u4ee3 GC \u662f ParNew\uff0c\u5373\u542f\u7528 CMS \u9ed8\u8ba4\u540c\u65f6\u6fc0\u6d3b  <code>-XX:+UseParNewGC<\/code> \u3002<\/p>\n<p>\u901a\u8fc7 <code>-XX:+CMSParallelInitialMarkEnabled<\/code> \u53c2\u6570\u53ef\u4ee5\u5f00\u542f\u8be5\u9636\u6bb5\u7684\u5e76\u884c\u6807\u8bb0\uff0c\u4f7f\u7528\u591a\u4e2a\u7ebf\u7a0b\u8fdb\u884c\u6807\u8bb0\uff0c\u51cf\u5c11\u6682\u505c\u65f6\u95f4\u3002<\/p>\n<p>\u5173\u95ed\u9884\u6e05\u7406\u9636\u6bb5\uff1a\u901a\u8fc7 <code>-XX:-CMSPrecleaningEnabled<\/code>\uff0c\u9ed8\u8ba4\u5f00\u542f\u3002<\/p>\n<h2>7.3 \u53ef\u4e2d\u65ad\u9884\u6e05\u7406\u76f8\u5173<\/h2>\n<p>\u65b0\u751f\u4ee3 Eden \u533a\u7684\u5185\u5b58\u4f7f\u7528\u91cf\u5927\u4e8e\u53c2\u6570 <code>-XX:CMSScheduleRemarkEdenSizeThreshold =2m<\/code> \u6267\u884c\u53ef\u4e2d\u65ad\u9884\u6e05\u7406\u3002<\/p>\n<p><code>-XX:CMSMaxAbortablePrecleanLoops=n<\/code> \uff1a\u8bbe\u7f6e\u6700\u591a\u5faa\u73af\u7684\u6b21\u6570\uff0c\u9ed8\u8ba4\u662f 0 \u8868\u793a\u6ca1\u6709\u9650\u5236\u3002<\/p>\n<p><code>-XX:CMSAbortablePrecleanTime=5<\/code> \u9650\u5236\u6267\u884c\u53ef\u4e2d\u65ad\u9884\u6e05\u7406\u7684\u6700\u957f\u65f6\u95f4\uff0c\u5355\u4f4d\u662f\u79d2\uff0c\u9ed8\u8ba4\u662f 5\uff0c\u8fbe\u5230\u8fd9\u4e2a\u65f6\u95f4\u9000\u51fa\u5faa\u73af\u3002<\/p>\n<p><code>-XX:CMSScheduleRemaikEdenPenetration=50<\/code> Eden \u533a\u7684\u4f7f\u7528\u7387\u8fbe\u5230\u8fd9\u4e2a\u767e\u5206\u6bd4\u9000\u51fa\u5faa\u73af\u3002<\/p>\n<h1>9. \u8c03\u4f18<\/h1>\n<h2>9.1 \u664b\u5347\u5931\u8d25<\/h2>\n<ul>\n<li>\u4ee4\u8001\u5e74\u4ee3\u56de\u6536\u5c3d\u65e9\u5f00\u59cb\uff0c\u589e\u5927\u56de\u6536\u9891\u7387\u3002<\/li>\n<li>\u589e\u5927\u8001\u5e74\u4ee3\u7a7a\u95f4\u3002<\/li>\n<li>\u589e\u5927\u65b0\u751f\u4ee3\u7a7a\u95f4\uff0c\u63d0\u9ad8\u5bf9\u8c61\u6ede\u7559\u65f6\u95f4\uff0c\u66f4\u591a\u7684\u5bf9\u8c61\u88ab\u56de\u6536\u800c\u4e0d\u662f\u664b\u5347\u3002<\/li>\n<li>\u589e\u52a0\u66f4\u591a\u7684\u540e\u53f0\u56de\u6536\u7ebf\u7a0b\u3002<\/li>\n<\/ul>\n<h2>9.2 \u5e76\u53d1\u6a21\u5f0f\u5931\u8d25<\/h2>\n<ul>\n<li>\u6709\u96be\u5ea6\uff0c\u56e0\u4e3aCMS\u672c\u8eab\u4e0d\u80fd Compat \u5185\u5b58\uff0c\u53ea\u80fd\u9000\u5316\u5230 SerialGC \u6765\u505a\u3002<\/li>\n<li>\u5c1d\u8bd5\u7528G1\uff0cG1\u7684\u5185\u5b58\u6a21\u578b\u66f4\u52a0\u5148\u8fdb\u3002JDK 11 \u5f15\u5165\u7684 ZGC \u5e94\u8be5\u662f\u66f4\u597d\u7684\u9009\u62e9\u3002<\/li>\n<\/ul>\n<h1>10. \u53c2\u8003\u8d44\u6599<\/h1>\n<p><a href=\"https:\/\/www.jianshu.com\/p\/b021d867627b\">JVM \u6e90\u7801\u89e3\u8bfb\u4e4b CMS GC \u89e6\u53d1\u6761\u4ef6<\/a><br \/>\n<a href=\"https:\/\/www.cnblogs.com\/yunxitalk\/p\/8977007.html\">CMS\u5783\u573e\u6536\u96c6\u5668<\/a><\/p>\n<h1>11. gc \u65e5\u5fd7<\/h1>\n<p>abortable-preclean  \u7b49\u6765\u4e86\u4e00\u6b21 YGC \uff1a<\/p>\n<pre><code>2019-12-19T10:08:59.836+0800: 9.146: [GC (CMS Initial Mark) [1 CMS-initial-mark: 29316K(174784K)] 35958K(253440K), 0.0018362 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] \n2019-12-19T10:08:59.838+0800: 9.148: [CMS-concurrent-mark-start]\n2019-12-19T10:08:59.867+0800: 9.177: [CMS-concurrent-mark: 0.029\/0.029 secs] [Times: user=0.13 sys=0.00, real=0.03 secs] \n2019-12-19T10:08:59.867+0800: 9.177: [CMS-concurrent-preclean-start]\n2019-12-19T10:08:59.868+0800: 9.178: [CMS-concurrent-preclean: 0.001\/0.001 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] \n2019-12-19T10:08:59.868+0800: 9.178: [CMS-concurrent-abortable-preclean-start]\n\n2019-12-19T10:09:00.050+0800: 9.360: [GC (Allocation Failure) 2019-12-19T10:09:00.050+0800: 9.360: [ParNew: 75352K-&gt;5384K(78656K), 0.0046068 secs] 104668K-&gt;35432K(253440K), 0.0046823 secs] [Times: user=0.06 sys=0.00, real=0.01 secs] \n\n2019-12-19T10:09:00.195+0800: 9.506: [CMS-concurrent-abortable-preclean: 0.142\/0.327 secs] [Times: user=1.15 sys=0.00, real=0.33 secs] \n2019-12-19T10:09:00.196+0800: 9.506: [GC (CMS Final Remark) [YG occupancy: 49922 K (78656 K)]2019-12-19T10:09:00.196+0800: 9.506: [Rescan (parallel) , 0.0108109 secs]2019-12-19T10:09:00.206+0800: 9.517: [weak refs processing, 0.0000196 secs]2019-12-19T10:09:00.206+0800: 9.517: [class unloading, 0.0058067 secs]2019-12-19T10:09:00.212+0800: 9.523: [scrub symbol table, 0.0079906 secs]2019-12-19T10:09:00.220+0800: 9.531: [scrub string table, 0.0008547 secs][1 CMS-remark: 30048K(174784K)] 79970K(253440K), 0.0260276 secs] [Times: user=0.05 sys=0.00, real=0.03 secs] \n2019-12-19T10:09:00.222+0800: 9.532: [CMS-concurrent-sweep-start]\n2019-12-19T10:09:00.230+0800: 9.541: [CMS-concurrent-sweep: 0.009\/0.009 secs] [Times: user=0.06 sys=0.00, real=0.01 secs] \n2019-12-19T10:09:00.230+0800: 9.541: [CMS-concurrent-reset-start]\n2019-12-19T10:09:00.231+0800: 9.541: [CMS-concurrent-reset: 0.001\/0.001 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] \n<\/code><\/pre>\n<p><code>[YG occupancy: 49922 K (78656 K)]<\/code> \u8868\u793a\u5e74\u8f7b\u4ee3\u7684\u4f7f\u7528\u60c5\u51b5\u3002<\/p>\n<p><code>[Rescan (parallel) , 0.0108109 secs]<\/code> \u8868\u793a\u91cd\u65b0\u6807\u8bb0\u9636\u6bb5\u5e76\u53d1\u626b\u63cf\u7684\u8017\u65f6\u3002<\/p>\n<p><code>[weak refs processing, 0.0000196 secs]<\/code> \u8868\u793a\u5bf9\u5f31\u5f15\u7528\u7684\u5904\u7406\u8017\u65f6\u3002<\/p>\n<p><code>[class unloading, 0.0058067 secs]<\/code> \u8868\u793a\u5378\u8f7d\u65e0\u7528\u7684\u7c7b\u7684\u8017\u65f6\u3002<\/p>\n<p><code>[scrub symbol table, 0.0079906 secs]<\/code> \u8868\u793a\u6e05\u7406\u5206\u522b\u5305\u542b\u7c7b\u7ea7\u5143\u6570\u636e\u548c\u5185\u90e8\u5316\u5b57\u7b26\u4e32\u7684\u7b26\u53f7\u548c\u5b57\u7b26\u4e32\u8868\u7684\u8017\u65f6\u3002<\/p>\n<p><code>[scrub string table, 0.0008547 secs]<\/code> \u6e05\u7406<\/p>\n<p><code>[1 CMS-remark: 30048K(174784K)] 79970K(253440K), 0.0260276 secs]<\/code> \u8868\u793a\u8001\u5e74\u4ee3\u3001\u6574\u4e2a\u5806\u7684\u5185\u5b58\u4f7f\u7528\u60c5\u51b5\u3002<\/p>\n<p>\u901a\u8fc7 <code>jmap -histo:live &lt;pid&gt;<\/code> \u89e6\u53d1\u7684 full gc<\/p>\n<pre><code>2019-12-19T10:53:04.251+0800: 81.175: [Full GC (Heap Inspection Initiated GC) 2019-12-19T10:53:04.251+0800: 81.175: [CMS: 61284K-&gt;57074K(174784K), 0.1813809 secs] 85360K-&gt;57074K(253440K), [Metaspace: 67599K-&gt;67599K(1110016K)], 0.1814978 secs] [Times: user=0.19 sys=0.00, real=0.18 secs] \n<\/code><\/pre>\n<p>\u5143\u7a7a\u95f4\u6269\u5bb9\u5bfc\u81f4\u7684 gc<\/p>\n<pre><code>2019-12-19T11:10:26.975+0800: 23.032: [Full GC (Metadata GC Threshold) 2019-12-19T11:10:26.975+0800: 23.032: [CMS2019-12-19T11:10:27.041+0800: 23.099: [CMS-concurrent-mark: 0.072\/0.072 secs] [Times: user=0.06 sys=0.00, real=0.07 secs] \n (concurrent mode failure): 56826K-&gt;55560K(174784K), 0.2376781 secs] 58594K-&gt;55560K(253504K), [Metaspace: 64259K-&gt;64259K(1107968K)], 0.2378476 secs] [Times: user=0.23 sys=0.00, real=0.24 secs] \n2019-12-19T11:10:27.213+0800: 23.270: [Full GC (Last ditch collection) 2019-12-19T11:10:27.213+0800: 23.270: [CMS: 55560K-&gt;49199K(174784K), 0.1635283 secs] 55560K-&gt;49199K(253504K), [Metaspace: 64259K-&gt;64259K(1107968K)], 0.1638558 secs] [Times: user=0.17 sys=0.00, real=0.16 secs] \n<\/code><\/pre>\n<p><code>Metadata GC Threshold<\/code>\uff1a\u8868\u793a metaspace \u7a7a\u95f4\u4e0d\u80fd\u6ee1\u8db3\u5206\u914d\u65f6\u89e6\u53d1\uff0c\u8fd9\u4e2a\u9636\u6bb5\u4e0d\u4f1a\u6e05\u7406\u8f6f\u5f15\u7528\uff1b<br \/>\n<code>Last ditch collection<\/code>\uff1a\u7ecf\u8fc7 <code>Metadata GC Threshold<\/code> \u89e6\u53d1\u7684 full gc \u540e\u8fd8\u662f\u4e0d\u80fd\u6ee1\u8db3\u6761\u4ef6\uff0c\u518d\u89e6\u53d1\u4e00\u6b21 gc cause \u4e3a <code>Last ditch collection<\/code> \u7684 full gc\uff0c\u8fd9\u6b21 full gc \u4f1a\u6e05\u7406\u8f6f\u5f15\u7528\u3002<\/p>\n<p>\u5404\u79cd GC \u7684\u89e6\u53d1\u539f\u56e0\u89e3\u91ca\u89c1\uff1a<a href=\"https:\/\/dzone.com\/articles\/java-gc-causes-distilled\">Java GC Causes Distilled<\/a><\/p>\n<hr \/>\n<p><code>-XX:+AlwaysTenure<\/code> YGC \u65f6 JVM \u76f4\u63a5\u628a\u5bf9\u8c61\u664b\u5347\u5230\u8001\u5e74\u4ee3\u800c\u4e0d\u662f\u62f7\u8d1d\u5230 survivor \u7a7a\u95f4\u3002<\/p>\n<p>\u664b\u5347\u7684\u4e24\u4e2a\u6761\u4ef6\uff1a\u5e74\u9f84\u8fbe\u5230 <code>\u2013XX:MaxTenuringThreshold<\/code> \u6216\u76ee\u6807 survivor \u7684\u4f7f\u7528\u7387\u8fbe\u5230 <code>\u2013XX:TargetSurvivorRatio<\/code> \u3002<\/p>\n<p><code>-XX:PretenureSizeThreshold=&lt;n&gt;<\/code> \u6307\u793a JVM \u628a\u5927\u5c0f\u5927\u4e8e n \u5b57\u8282\u7684\u5bf9\u8c61\u76f4\u63a5\u5206\u914d\u5230\u8001\u5e74\u4ee3\u3002<br \/>\n\u5982\u679c\u5bf9\u8c61\u7684\u5927\u5c0f\u5927\u4e8e eden \u7a7a\u95f4\u4e5f\u4f1a\u76f4\u63a5\u5206\u914d\u5230\u8001\u5e74\u4ee3\u3002<br \/>\n\u7cfb\u7edf\u5bf9\u8c61\u603b\u662f\u76f4\u63a5\u5206\u914d\u5230\u6c38\u4e45\u4ee3\u3002<\/p>\n<hr \/>\n<p>\u6b22\u8fce\u5173\u6ce8\u6211\u7684\u5fae\u4fe1\u516c\u4f17\u53f7: <strong>coderbee\u7b14\u8bb0<\/strong> \u3002<br \/>\n<img loading=\"lazy\" decoding=\"async\" width=\"258\" height=\"258\" src=\"https:\/\/coderbee.net\/wp-content\/uploads\/2019\/01\/coderbee-note.jpg\" class=\"alignnone size-full wp-image-1707\" \/><\/p>\n","protected":false},"excerpt":{"rendered":"<p>1. \u6982\u8ff0 CMS\uff0cMost concurrently\uff0c\u662f\u4e00\u6b3e \u91c7\u7528 \u5e76\u53d1-\u6807\u8bb0 &hellip; <a href=\"https:\/\/coderbee.net\/index.php\/jvm\/20200103\/2056\">\u7ee7\u7eed\u9605\u8bfb <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[96],"tags":[339,101,233],"_links":{"self":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/2056"}],"collection":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/comments?post=2056"}],"version-history":[{"count":3,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/2056\/revisions"}],"predecessor-version":[{"id":2061,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/2056\/revisions\/2061"}],"wp:attachment":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/media?parent=2056"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/categories?post=2056"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/tags?post=2056"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}