Java Heapdump

Java Heapdump

Generate Heapdump for Sun JDK:
Generate Heapdump for IBM JDK 1.4
set IBM_HEAP_DUMP=true

Setting either of these to any value (such as true) enables heap dump production by means of signals.
When set to TRUE or 1 - generates a heapdump each time an out-of-memory exception is thrown, even if it is handled.
When set to TRUE or 1 - generates a Javadump each time an out-of-memory exception is thrown, even if it is handled.
Specify an alternative location for Heapdump files.
Specify an alternative location for Javadump files

Use this environment variable to cause the JVM to generate a text (human readable) Heapdump.

Use this environment variable to control the conditions under which Heapdumps (and other dumps) are produced.

The recommended way of controlling the production of diagnostic data is the -Xdump command-line option. However, if you do use JAVA_DUMP_OPTS, the recommended default value is:
see Using Heapdump
Using Heapdump
Heapdump is an IBM JVM facility that generates a dump of all the reachable objects that are on the Java heap. It shows the objects that are using large amounts of memory on the Java heap, and what is preventing them from being collected by the Garbage Collector.

You can generate a Heapdump in either of two ways:
Explicit generation
JVM-triggered generation
Explicit generation of a Heapdump
You can explicitly generate a Heapdump in either of the following ways:
By sending a signal to the JVM from the operating system
By using the HeapDump() method inside Java code that is being executed

For Linux and AIX, send the JVM the signal SIGQUIT (kill -QUIT or -3, or Ctrl+\ in the console window): kill -3 proceessID
For Windows, generate a SIGINT (press the Ctrl+Break keys simultaneously).
You can explicitly request a Heapdump from a Java method. The class contains a static HeapDump() method that causes Java code to initiate a Heapdump, provided that the IBM_HEAPDUMP environment variable is set.
Triggered generation of a Heapdump
The following events automatically trigger the JVM to produce a Heapdump:
A fatal native exception occurs in the JVM (not a Java Exception)
An OutOfMemory or heap exhaustion condition occurs (optional)
Location of the generated Heapdump
The location that is specified by the IBM_HEAPDUMPDIR environment variable,if set (_CEE_DMPTARG on z/OS).
The current working directory of the JVM processes
The location that is specified by the TMPDIR environment variable, if set
The /tmp directory (X:\tmp for Windows, where X is the current working drive)
Format of Heapdump filenames
Windows heapdump.YYYYMMDD.HHMMSS.PID.txt
Linux & AIX heapdumpPID.TIME.txt
Note: PID is the process ID. TIME is the number of seconds since 1/1/1970
Using VerboseGC to obtain heap information
Use the VerboseGC utility to obtain information about the Java Object heap in real time while running your Java applications. To activate this utility, run Java with the -verbosegc option:
java -verbosegc

JVM environment settings -- general options
Heap size
The maximum heap size is controlled by the -Xmx option.
The initial size of the heap is controlled by the -Xms option.
A list of directories for the JVM to find user class files, paths, or both to individual Java archive or .compressed files that contain class files

Heapdump or JavaCore Analyze Tools:
Eclipse Memory Analyzer (MAT)
The Eclipse Memory Analyzer is a fast and feature-rich Java heap analyzer that helps you find memory leaks and reduce memory consumption.
IBM HeapAnalyzer
HeapAnalyzer analyzes Java heap dumps by parsing the Java heap dump, creating directional graphs, transforming them into directional trees, and executing the heuristic search engine.
IBM Thread and Monitor Dump Analyzer for Java:jca
A tool that allows identification of hangs, deadlocks, resource contention, and bottlenecks in Java threads.

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