{"id":1198,"date":"2009-09-25T22:40:08","date_gmt":"2009-09-26T03:40:08","guid":{"rendered":"http:\/\/jianmingli.com\/wp\/?p=1198"},"modified":"2011-08-02T09:23:45","modified_gmt":"2011-08-02T14:23:45","slug":"jvm","status":"publish","type":"post","link":"https:\/\/jianmingli.com\/wp\/?p=1198","title":{"rendered":"JVM 1.5"},"content":{"rendered":"

Intro<\/h2><\/span>\n

JVM<\/h3><\/span>\n

* myfile.java — Compiler (javac) –> Byte code — java.exe –> JVM — OS –> Native code<\/p>\n

GC<\/h3><\/span>\n

Sun JVM is generational and divides heap into<\/h4><\/span>\n

* Young Generation
\n– Eden Space
\n– Survivor Space 0 (aka From Space)
\n– Survivor Space 1 (aka To Space)
\n* Old Generation
\n* Permanent Generation: holds class files<\/p>\n

GC Process<\/h4><\/span>\n

* All objects are created in Eden Space
\n* When Eden Space fills up, JVM triggers a minor GC:
\n– All unreferenced objects in Eden Space are freed
\n– All live objects are copies to S0 until S0 is full. Left over objects are copied to Old Generation.
\n* When Old Generation fills up, JVM triggers a major GC, aka mark-and-sweep:
\n– All threads are frozen
\n– All unreachable objects in Old Generation are freed (construct root-set, reachability test, free unreachable objects, defragment heap)<\/p>\n

JVM Parameters<\/h4><\/span>\n

-Xmxm # Max heap in mb
\n-Xmsm # Min heap in mb
\n-XX:NewSize=m # Young generation size in mb
\n-XX:MaxNewSize=m # Max young generation size in mb
\n-XX:SurvivorRatio= # Eden to survivor ratio
\n-XX:PermSize=m # Initial permanent generation size
\n-XX:MaxPermSize=NNNm # Max permanent generation size<\/p>\n

Configure Web Based Application JVM Heap<\/h4><\/span>\n

* Young Generation = 3\/8 Heap
\n* S0 = 1\/6 Young Generation
\n* S1 = 1\/20 Young Generation<\/p>\n

\r\njava -Xmx1024m -Xms1024m -XX:NewSize=448m -XX:MaxNewSize=448m -XX:SurvivorRatio=6 -XX:PermSize=128m -XX:MaxPermSize=128m\r\n<\/pre>\n
Garbage Collector Policy<\/h4><\/span>\n
* The -XX:+UseParallelGC parallel (throughput) garbage collector
\n* The -XX:+UseConcMarkSweepGC concurrent (low pause time) garbage collector (also known as CMS)
\n* The -XX:+UseSerialGC serial garbage collector (for smaller applications and systems) <\/p>\n
Visual GC<\/h2><\/span>\n
* Download Visual GC from http:\/\/java.sun.com\/performance\/jvmstat\/#Download<\/a>
\n* Unzip
\n* Set JVMSTAT_JAVA_HOME env <\/p>\n
set JVMSTAT_JAVA_HOME=\"C:\\Program Files\\Java\\jdk1.5.0_14\"<\/pre>\n
* Make sure java -version returns 1.5 or higher<\/p>\n
\r\nC:\\WINDOWS\\system32>java -version\r\njava version \"1.5.0_14\"\r\nJava(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_14-b03)\r\nJava HotSpot(TM) Client VM (build 1.5.0_14-b03, mixed mode)\r\n<\/pre>\n
* Find jvmid with jps command<\/p>\n
\r\njps\r\n4964 SoapUI\r\n6024 Jps\r\n1224 Bootstrap\r\n<\/pre>\n
* Launch VisualGC<\/p>\n
visualgc.cmd 1224<\/pre>\n
References<\/h2><\/span>\n
http:\/\/www.informit.com\/guides\/content.aspx?g=java&seqNum=253<\/a>
\nJava Tuning White Paper<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
Intro JVM * myfile.java — Compiler (javac) –> Byte code — java.exe –> JVM — OS –> Native code GC Sun JVM is generational and divides heap into * Young Generation – Eden Space – Survivor Space 0 (aka From … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[14],"tags":[],"class_list":["post-1198","post","type-post","status-publish","format-standard","hentry","category-java"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/s8cRUO-jvm","_links":{"self":[{"href":"https:\/\/jianmingli.com\/wp\/index.php?rest_route=\/wp\/v2\/posts\/1198","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/jianmingli.com\/wp\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/jianmingli.com\/wp\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/jianmingli.com\/wp\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/jianmingli.com\/wp\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1198"}],"version-history":[{"count":9,"href":"https:\/\/jianmingli.com\/wp\/index.php?rest_route=\/wp\/v2\/posts\/1198\/revisions"}],"predecessor-version":[{"id":2906,"href":"https:\/\/jianmingli.com\/wp\/index.php?rest_route=\/wp\/v2\/posts\/1198\/revisions\/2906"}],"wp:attachment":[{"href":"https:\/\/jianmingli.com\/wp\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1198"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/jianmingli.com\/wp\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1198"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/jianmingli.com\/wp\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1198"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}