Compare snapshots

One heap dump shows what is alive at one moment. It cannot say whether a number is growing, because it has no "before". These modes compare dumps of the same process: a pair for a clear before-and-after, or a series of three or more for a timeline.

Start here

• Two dumps around one action: Snapshot diff.
• Three or more, in order: Diff a series. It finds the classes that never shrink.
• Android memory that does not live in the Java heap: Native context.

Your goal, and the page

Your goal	Command	Page
What changed between two dumps?	--diff-from a.hprof --diff-to b.hprof	Snapshot diff
What keeps growing across a timeline?	--diff-series a.hprof b.hprof c.hprof	Diff a series
Is it Java heap growth or native?	--native-context meminfo.txt	Native context
Capture the dumps	android-capture --series 3	Capture a series

Recipes

Your problem	Recipe
Memory grows while media plays	Playback growth
I want to know what one screen or action costs	Before and after an interaction

What a comparison can and cannot tell you

• It compares classes, not objects. Object ids are not stable between dumps, so heaptrail counts instances and shallow bytes per class name, and compares those totals.
• It is shallow. A diff shows growth in the bytes objects occupy themselves. Use --retained-size on one dump to see what the growth keeps alive.
• It needs the same build. Obfuscated names change between builds, so compare dumps of one build, or restore names with --mapping first.
• A diff is a signal, not a proof. Growth between two dumps taken seconds apart may be warm-up. Capture around a deliberate, repeatable action, and prefer a series.

Related

• Capture a series takes the dumps.
• Analyze for what to do with one dump.
• Trace holders for what to do with a class a diff points at.