What is 'remainder'?

[youngledo]

I see that 'remainder' occupies a certain size on the interface, but I cannot see what it actually has. Can you explain what it is and when it will appear?

At times, its proportion is still significant, but I cannot see why it is so large.

[kgibm]

"Remainder" is a generic feature of pie charts in MAT when the sum of slices don't add up to the total heap usage the pie chart represents: https://github.com/eclipse-mat/mat/blob/R_1.15.0/plugins/org.eclipse.mat.api/src/org/eclipse/mat/snapshot/query/PieFactory.java#L228-L233

The specific pie chart you're showing is the Top Consumers query in the addBiggestObjects method: https://github.com/eclipse-mat/mat/blob/R_1.15.0/plugins/org.eclipse.mat.api/src/org/eclipse/mat/inspections/TopConsumers2Query.java#L169

Basically that's going through the top level of the dominator tree and adding a pie slice if the retained heap of a dominator is greater than a percentage of the total heap (default = 1%).

So the large remainder in the second chart means that there are no large dominators consuming a majority of the heap. This is common with complex object graphs. When the dominator tree isn't useful, then the next steps include the histogram, leak suspects report, etc.: https://help.eclipse.org/latest/topic/org.eclipse.mat.ui.help/gettingstarted/basictutorial.html

[youngledo]

Thanks, isn't this remainder also part of the heap, don't you need to pay attention to this memory?

[kgibm]

Thanks, isn't this remainder also part of the heap, don't you need to pay attention to this memory?

Yes. The remaining dominators didn't exceed 1% of the heap so generally in this case the recommendation is to review other queries in MAT: https://help.eclipse.org/latest/topic/org.eclipse.mat.ui.help/gettingstarted/basictutorial.html

If none of those core queries help, generally what I do then is to go to the Histogram, sort by retained heap, find the largest non-JDK & non-framework classes, right click, Merge Shortest Paths to GC roots excluding phantom/soft/weak/etc. references and then calculate the minimum retained heap for referenced objects and explore the shortest paths to GC roots that retains the most of these.