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101 lines
3.4 KiB
101 lines
3.4 KiB
# Memory: Java heap profiler
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NOTE: The Java heap profiler requires Android 11 or higher
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See the [Memory Guide](/docs/case-studies/memory.md#java-hprof) for getting
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started with Java heap profiling.
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Conversely from the [Native heap profiler](native-heap-profiler.md), the Java
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heap profiler reports full retention graphs of managed objects but not
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call-stacks. The information recorded by the Java heap profiler is of the form:
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_Object X retains object Y, which is N bytes large, through its class member
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named Z_.
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## UI
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Heap graph dumps are shown as flamegraphs in the UI after clicking on the
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diamond in the _"Heap Profile"_ track of a process. Each diamond corresponds to
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a heap dump.
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## SQL
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Information about the Java Heap is written to the following tables:
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* [`heap_graph_class`](/docs/analysis/sql-tables.autogen#heap_graph_class)
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* [`heap_graph_object`](/docs/analysis/sql-tables.autogen#heap_graph_object)
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* [`heap_graph_reference`](/docs/analysis/sql-tables.autogen#heap_graph_reference)
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For instance, to get the bytes used by class name, run the following query.
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As-is this query will often return un-actionable information, as most of the
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bytes in the Java heap end up being primitive arrays or strings.
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```sql
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select c.name, sum(o.self_size)
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from heap_graph_object o join heap_graph_class c on (o.type_id = c.id)
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where reachable = 1 group by 1 order by 2 desc;
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```
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|name |sum(o.self_size) |
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|--------------------|--------------------|
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|java.lang.String | 2770504|
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|long[] | 1500048|
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|int[] | 1181164|
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|java.lang.Object[] | 624812|
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|char[] | 357720|
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|byte[] | 350423|
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We can use `experimental_flamegraph` to normalize the graph into a tree, always
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taking the shortest path to the root and get cumulative sizes.
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Note that this is **experimental** and the **API is subject to change**.
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From this we can see how much memory is being held by each type of object
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For that, we need to find the timestamp and upid of the graph.
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```sql
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select distinct graph_sample_ts, upid from heap_graph_object
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```
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graph_sample_ts | upid |
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--------------------|--------------------|
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56785646801 | 1 |
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We can then use them to get the flamegraph data.
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```sql
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select name, cumulative_size
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from experimental_flamegraph(56785646801, 1, 'graph')
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order by 2 desc;
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```
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| name | cumulative_size |
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|------|-----------------|
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|java.lang.String|1431688|
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|java.lang.Class<android.icu.text.Transliterator>|1120227|
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|android.icu.text.TransliteratorRegistry|1119600|
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|com.android.systemui.statusbar.phone.StatusBarNotificationPresenter$2|1086209|
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|com.android.systemui.statusbar.phone.StatusBarNotificationPresenter|1085593|
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|java.util.Collections$SynchronizedMap|1063376|
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|java.util.HashMap|1063292|
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## TraceConfig
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The Java heap profiler is configured through the
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[JavaHprofConfig](/docs/reference/trace-config-proto.autogen#JavaHprofConfig)
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section of the trace config.
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```protobuf
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data_sources {
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config {
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name: "android.java_hprof"
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java_hprof_config {
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process_cmdline: "com.google.android.inputmethod.latin"
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dump_smaps: true
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}
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}
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}
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```
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