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Indicating how old an object is [message #1691505] Tue, 07 April 2015 16:33 Go to next message
Mark Robbins is currently offline Mark RobbinsFriend
Messages: 2
Registered: April 2015
Junior Member
Hello,

Is there any way that the MAT can indicate how old an object is?
Alternatively is there a way that the MAT can identify which area the object is in if the gencon policy is in use (e.g. nursery or tenured)?

sometimes there are large numbers of class instances in memory if there has been a bad memory leak.

I cross reference with application logs to try to identify likely events that generated the objects. It would help if there were some indicators about how old an object is so I can rule out very recent events.

I'm guessing from other conversations that the JVM doesn't store the creation time with the object and just stores some kind of number indicating how many cycles the object has survived.

thanks,

Mark

[Updated on: Mon, 13 April 2015 16:17]

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Re: Indicating how old an object is [message #1692121 is a reply to message #1691505] Mon, 13 April 2015 16:16 Go to previous message
Mark Robbins is currently offline Mark RobbinsFriend
Messages: 2
Registered: April 2015
Junior Member
I have had discussions and the gist of the discussions are this:

Objects in the nursery contain a flip count that is incremented during the GC.
When the flip count reaches a threshold then the GC moves the object into the tenured area.

Once it is in that area there is no similar count for the length of time that the object has been in the tenured area.

The cost of adding a timestamp to each object would be too expensive.

For later readers who need to look at the heap in real time then the IBM Health Center provides a capability to monitor the heap/objects in real time.

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