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
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.
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.
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 |
We can use experimental_flamegraph
to normalize the graph into a tree, always taking the shortest path to the root and get cumulative sizes. Note that this is experimental and the API is subject to change. From this we can see how much memory is being held by each type of object
For that, we need to find the timestamp and upid of the graph.
select distinct graph_sample_ts, upid from heap_graph_object
graph_sample_ts | upid |
---|---|
56785646801 | 1 |
We can then use them to get the flamegraph data.
select name, cumulative_size from experimental_flamegraph where ts = 56785646801 and upid = 1 and profile_type = 'graph' order by 2 desc;
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 |
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 } } }