How to automatically get retained memory while profiling in JProfiler offline mode with triggers

Question

I have a large, memory-intensive, Java-based web application with many different features that will take me a long time to profile. Instead of manually profiling every feature in the entire application with different test data, I'm thinking a more time-efficient approach is to run JProfiler in offline mode and set up triggers to capture data for me. Testing teams will use the software normally, and over time, JProfiler will capture memory-intsensive hotspots that we can use to make our application more efficient.

However, if I set up a trigger to just take a Snapshot of the heap, then it will only give me the shallow memory -- the memory stats of each class, excluding any referenced objects it contains. But it's not useful to me to know how much memory is consumed by instances of String or char[]. What I really want to know is the retained memory of my classes -- the memory of the shallow size of each instance plus all classes that it contains. In other words, for each class in my software, I want to know how much memory will be freed when all its instances are garbage collected.

So basically I have a few questions:

1) Can JProfiler calculate the retained memory by just triggering snapshots without recording the memory? It seems that you have to actually perform the "record memory" action to calculate the retained memory, but I might be missing something.

2) If I have to record memory to calculate the retained memory information, then my next thought was to set up a trigger to record the information when the overall memory reached a certain threshold. But this raises two more questions: how will I set up a trigger to stop the recording and take a snapshot? And won't the recording miss the most important memory information since we're already past the threshold specified in the trigger?

Number 2 from above leads me to believe that the best way to profile is to trigger snapshots without any recording and calculating of retained memory -- so shallow memory only. However, if the shallow memory shows that most of my memory usage is in char[] (which it does), how can I get useful information out of this? How does this help me track down memory intensive areas of my application?

Any help is greatly appreciated

Answer 1

1) Can JProfiler calculate the retained memory by just triggering snapshots without recording the memory? It seems that you have to actually perform the "record memory" action to calculate the retained memory, but I might be missing something.

You actually need the "Trigger heap dump" action, then the heap walker will be available. The "Start recording" action with "Allocation data" enabled records data for the live views (where only the shallow size is available), but it also provides data for the "Allocations" view of the heap walker, so you can analyze where objects were allocated.

And won't the recording miss the most important memory information since we're already past the threshold specified in the trigger?

The heap dump captures the entire heap at the moment in time when the trigger is fired, so you should see all objects of interest.