Memory: Java heap dumps

NOTE: Capturing Java heap dumps requires Android 11 or higher

See the Memory Guide for getting started with Java heap dumps.

Conversely from Native heap profiles, Java heap dumps report full retention graphs of managed objects but not call-stacks. The information recorded in a Java heap dump is of the form: Object X retains object Y, which is N bytes large, through its class member named Z.

Java heap dumps are not to be confused with profiles taken by the Java heap sampler

UI

Heap graph dumps are shown as flamegraphs in the UI after clicking on the diamond in the "Heap Profile" track of a process. Each diamond corresponds to a heap dump.

Flamegraph of a Java heap dump

The native size of certain objects is represented as an extra child node in the flamegraph, prefixed with "[native]". The extra node counts as an extra object. This is available only on Android 13 or higher.

SQL

Information about the Java Heap is written to the following tables:

native_size (available only on Android T+) is extracted from the related libcore.util.NativeAllocationRegistry and is not included in self_size.

For instance, to get the bytes used by class name, run the following query. As-is this query will often return un-actionable information, as most of the bytes in the Java heap end up being primitive arrays or strings.

select c.name, sum(o.self_size)
       from heap_graph_object o join heap_graph_class c on (o.type_id = c.id)
       where reachable = 1 group by 1 order by 2 desc;

name	sum(o.self_size)
java.lang.String	2770504
long[]	1500048
int[]	1181164
java.lang.Object[]	624812
char[]	357720
byte[]	350423

Using the standard library, we can query the normalize the graph into a tree, always taking the shortest path to the root and get cumulative sizes. From this we can see how much memory is being held by each type of object

INCLUDE PERFETTO MODULE android.memory.heap_graph.class_summary_tree;

SELECT
  -- The name of the class.
  name,
  -- The sum of `self_size` of this node and all descendants of this node.
  cumulative_size
FROM android_heap_graph_class_summary_tree;

name	cumulative_size
java.lang.String	1431688
java.lang.Class<android.icu.text.Transliterator>	1120227
android.icu.text.TransliteratorRegistry	1119600
com.android.systemui.statusbar.phone.StatusBarNotificationPresenter$2	1086209
com.android.systemui.statusbar.phone.StatusBarNotificationPresenter	1085593
java.util.Collections$SynchronizedMap	1063376
java.util.HashMap	1063292

TraceConfig

The Java heap dump data source is configured through the JavaHprofConfig section of the trace config.

data_sources {
  config {
    name: "android.java_hprof"
    java_hprof_config {
      process_cmdline: "com.google.android.inputmethod.latin"
      dump_smaps: true
    }
  }
}