Odd heapdump

[Former Member]

I opened a heap dump generated from an OutOfMemory in IBM JVM verion 1.4, and then I tried to look into the content of heap rather than leak analysis, find large chunk etc because I know that it was a BIG BI request hit down the server node. So I just want to get the "context" of the thread which was executing the BI query.

I tried run the following OQL:

SELECT toString(s), s.count, s.value FROM java.lang.String s

I got more than 2 million results, but all of them are empty string, all char[] value are "\u0000"

Anyone knows why?

Thanks,

Denny

[krumts · Accepted solution]

Hi Denny,

The first possible reason that comes to my mind is that you have opened a .phd heap dump. PHD dumps are smaller in size, but they do not contain all the data, e.g. they don't contain the names of object fields and also the values of primitive fields (and primitive arrays) are missing. Therefore the String contents can't be restored.

So, are you using a .phd dump? If so, you could try using a system dump from the IBM JVM, pre-process it with jextract and then open it with Memory Analyzer. These dumps contain all object details. The relevant SAP notes (for different IBM platforms) about how to get and pre-process such dumps from a NetWeaver Java server you can find at the bottom of this page:

http://wiki.sdn.sap.com/wiki/pages/viewpage.action?pageId=33456.

Or are you already using a system dump?

Regards,

Krum

[Former Member · Accepted solution]

Thanks Krum, it's generated from IBM JVM 1.4.2 (J9) on AIX platform, and it's phd dump rather than system dump.

I mixed up my experience with HPROF and PHD, sorry about that.

[krumts · Accepted solution]

Hi,

Nothing to be sorry about. I guess it is most of the times good that we offer the same interface and queries regardless of the format, but I agree this could also be confusing. There are some queries which would check the format and show a popup that they can't work with a PDH dump. This is not the case for the OQL. I will consider if we can somehow warn the user.

Any suggestions are welcome.

Krum