CODEWITHSUNDEEP
javagarbage-collectionheap-memory
Colin
Colin

Reputation: 1162

How can I take a heap dump on Java 5 without garbage collecting first?

We have a long running server application running Java 5, and profiling it we can see the old generation growing slowly over time. It's correctly freed on a full GC, but I'd like to be able to look at the unreachable objects in Eclipse MAT using a heap dump. I've successfully obtained a heap dump using +XX:HeapDumpOnCtrlBreak, but the JVM always does a GC before dumping the heap. Apparently this doesn't happen on Java 6 but we're stuck on 5 for now. Is there any way to prevent this?

Upvotes: 13

Views: 16555

Answers (5)

daggett
daggett

Reputation: 28634

use jconsole or visualvm or jmc or ... other jmx management console. open HotSpotDiagnostic in com.sun.management. select method dumpHeap and input two parameters:

  • path to the dump file
  • (true/false) dump only live objects. use false to dump all objects.

Note that the dump file will be written by the JVM you connected to, not by JVisualVM, so if the JVM is running on a different system, it will be written on that system.

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Upvotes: 16

Robert Höglund
Robert Höglund

Reputation: 979

Have you tried the standard jmap tool shipped with the JDK? The jmap toll was officially introduced in Java 5.

Example command line: /java/bin/jmap -heap:format=b

The result can be processed with the standard jhat tool or with GUI applications such as MAT.

Upvotes: 4

Peter Thomas
Peter Thomas

Reputation: 58098

I have some code here that can programmatically take a heap dump over JMX:

Link: JmxHeapDumper.java

The comments in the source code contain 2 links to articles that contained useful information about how to take heap dumps. I don't know for sure but if you are in luck, perhaps the JMX approach would have some way of avoiding the GC. Hope this helps !

Upvotes: 3

L. Cornelius Dol
L. Cornelius Dol

Reputation: 64065

jProfiler (ej-technologies) can do this.

Upvotes: -1

skaffman
skaffman

Reputation: 403581

I suggest a 3rd-party profiler such as YourKit, which may allow you to take snapshots without kicking off the GC first. Added bonus, you can take a snapshot without the whole ctrl-break shenanigans.

Upvotes: 1

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