Thursday, March 20

Memory spaces in jdks:

Memory spaces in jdks:

Sun JDK has the following memory spaces: Eden space, survivior space, tenured generation and permanent generation. The objects move from one space to another according to its age and survival from garbage collection.

JRockit has 2 spaces, young generation and old generation, it uses the same mechanism of garbage collection. There is nothing called as permanent generation in JRockit.

JVM Crashes:

When JRockit crashes, a JRockit dump is produced which basically has the reason for the crash. JRockit uses native libraries by default. This can be disabled by disabling the NativeIO from the admin console.

A sun jdk crash produces hs_err_pid file which has the root cause of the crash. There can be several reasons for sun jdk crash are due to bugs in them (defects in the code of the jdk). These issues need to be reported to the sun team.

Tools for performance tracking:

Sun jdk that comes bundled with weblogic server gives tools like JConsole which can be used for performance tracking and monitoring the memory in use of the JVM. This tool is very much necessary so that each and every detail about the memory being used by the application, cpu usage, memory leaks can be identified.

Oracle JRockit has a much more advanced tool JRMC (JRockit mission Control) which gives advanced tracking features. JRA recordings can be taken which gives each detail about the JVM arguements, garbage collection details, methods using the maximum memory etc. The memory leak detector tool in JRMC is also one important and very helpful tool. These make it easy for the user and administrators to maintain a record and identify the issues with the application and the JVM.

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