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View the Java Heap and Memory Allocations with Memory Profiler

The Memory Profiler is a component in the Android Profiler that helps you identify memory leaks and memory churn that can lead to stutter, freezes, and even app crashes. It shows a realtime graph of your app's memory use, lets you capture a heap dump, force garbage collections, and track memory allocations.

To open the Memory Profiler, follow these steps:

  1. Click View > Tool Windows > Android Profiler (you can also click Android Profiler in the toolbar).
  2. Select the device and app process you want to profile from the Android Profiler toolbar. If you've connected a device over USB but don't see it listed, ensure that you have enabled USB debugging.
  3. Click anywhere in the MEMORY timeline to open the Memory Profiler.

Alternatively, you can inspect your app memory from the command line with dumpsys, and also see GC events in logcat.

Why you should profile your app memory

Android provides a managed memory environment—when it determines that your app is no longer using some objects, the garbage collector releases the unused memory back to the heap. How Android goes about finding unused memory is constantly being improved, but at some point on all Android versions, the system must briefly pause your code. Most of the time, the pauses are imperceivable. However, if your app allocates memory faster than the system can collect it, your app might be delayed while the collector frees enough memory to satisfy your allocations. The delay could cause your app to skip frames and cause visible slowness.

Even if your app doesn't exhibit slowness, if it leaks memory, it can retain that memory even while it's in the background. This behavior can slow the rest of the system's memory performance by forcing unnecessary garbage collection events. Eventually, the system is forced to kill your app process to reclaim the memory. Then when the user returns to your app, it must restart completely.

To help prevent these problems, you should use the Memory Profiler to do the following:

For information about programming practices that can reduce your app's memory use, read Manage Your App's Memory.

Memory Profiler overview

When you first open the Memory Profiler, you'll see a detailed timeline of your app's memory use and access tools to force garbage collection, capture a heap dump, and record memory allocations.

Figure 1. The Memory Profiler

As indicated in figure 1, the default view for the Memory Profiler includes the following:

  1. A button to force a garbage collection event.
  2. A button to capture a heap dump.
  3. A button to record memory allocations. This button appears only when connected to a device running Android 7.1 or lower.
  4. Buttons to zoom in/out of the timeline.
  5. A button to jump forward to the live memory data.
  6. The event timeline, which shows the activity states, user input events, and screen rotation events.
  7. The memory use timeline, which includes the following:
    • A stacked graph of how much memory is being used by each memory category, as indicated by the y-axis on the left and the color key at the top.
    • A dashed line indicates the number of allocated objects, as indicated by the y-axis on the right.
    • An icon for each garbage collection event.

However, if you're using a device running Android 7.1 or lower, not all profiling data is visible by default. If you see a message that says, "Advanced profiling is unavailable for the selected process," you need to enable advanced profiling to see the following:

On Android 8.0 and higher, advanced profiling is always enabled for debuggable apps.

How memory is counted

The numbers you see at the top of the Memory Profiler (figure 2) are based on all the private memory pages that your app has committed, according to the Android system. This count does not include pages shared with the system or other apps.

Figure 2. The memory count legend at the top of the Memory Profiler

The categories in the memory count are as follows:

When compared to memory counts from the previous Android Monitor tool, the new Memory Profiler records your memory differently, so it might seem like your memory use is now higher. The Memory Profiler monitors some extra categories that increase the total, but if you only care about the Java heap memory, then the "Java" number should be similar to the value from the previous tool.

And although the Java number probably doesn't exactly match what you saw in Android Monitor, the new number accounts for all physical memory pages that have been allocated to your app's Java heap since it was forked from Zygote. So this provides an accurate representation of how much physical memory your app is actually using.

View memory allocations

Memory allocations show you how each object in your memory was allocated. Specifically, the Memory Profiler can show you the following about object allocations:

If your device is running Android 8.0 or higher, you can view your object allocations at any time as follows: Just click-and-hold in the timeline and drag to select the region where you want to view the allocations (as shown in video 1). There's no need to begin a recording session because Android 8.0 and higher includes an on-device profiling tool that constantly tracks your app's allocations.

Video 1. With Android 8.0 and higher, select an existing timeline area to view object allocations

If your device is running Android 7.1 or lower, click Record memory allocations in the Memory Profiler toolbar. While recording, Android Monitor tracks all allocations that occur in your app. When you're done, click Stop recording (the same button; see video 2) to view the allocations.

Video 2. With Android 7.1 and lower, you must explicitly record memory allocations

Once you select a region of the timeline (or when you finish a recording session with a device running Android 7.1 or lower), the list of allocated objects appears below the timeline, grouped by class name and sorted by their heap count.

To inspect the allocation record, follow these steps:

  1. Browse the list to find objects that have unusually large heap counts and that might be leaked. To help find known classes, click the Class Name column header to sort alphabetically. Then click a class name. The Instance View pane appears on the right, showing each instance of that class, as shown in figure 3.
  2. In the Instance View pane, click an instance. The Call Stack tab appears below, showing where that instance was allocated and in which thread.
  3. In the Call Stack tab, click on any line to jump to that code in the editor.

Figure 3. Details about each allocated object appear in the Instance View on the right

By default, the list of allocations on the left is arranged by class name. At the top of the list, you can use the drop-down on the right to switch between the following arrangements:

Capture a heap dump

A heap dump shows which objects in your app are using memory at the time you capture the heap dump. Especially after an extended user session, a heap dump can help identify memory leaks by showing objects still in memory that you believe should no longer be there. Once you capture a heap dump, you can view the following:

To capture a heap dump, click Dump Java heap in the Memory Profiler toolbar. While dumping the heap, the amount of Java memory might increase temporarily. This is normal because the heap dump occurs in the same process as your app and requires some memory to collect the data.

The heap dump appears below the memory timeline, showing all class types in the heap, as shown in figure 4.

Figure 4. Viewing the heap dump

If you need to be more precise about when the dump is created, you can create a heap dump at the critical point in your app code by calling dumpHprofData().

In the list of classes, you can see the following information:

At the top of the class list, you can use the left drop-down list to switch between the following heap dumps:

The list of objects in the heap are arranged by class name, by default. You can use the other drop-down to switch between the following arrangements:

The list is sorted by the Retained Size column, by default. You can click on any of the column headers to change how the list is sorted.

Click a class name to open the Instance View window on the right (shown in figure 5). Each listed instance includes the following:

Figure 5. The duration required to capture a heap dump is indicated in the timeline

To inspect your heap, follow these steps:

  1. Browse the list to find objects that have unusually large heap counts and that might be leaked. To help find known classes, click the Class Name column header to sort alphabetically. Then click a class name. The Instance View pane appears on the right, showing each instance of that class, as shown in figure 5.
  2. In the Instance View pane, click an instance. The References tab appears below, showing every reference to that object.

    Or, click the arrow next to the instance name to view all its fields, and then click a field name to view all its references. And if you want to view the instance details for a field, right-click on the field and select Go to Instance.

  3. In the References tab, if you identify a reference that might be leaking memory, right-click on it and select Go to Instance. This selects the corresponding instance from the heap dump, showing you its own instance data.

In your heap dump, look for memory leaks caused by any of the following:

Save the heap dump as HPROF

Once you capture a heap dump, the data is viewable in the Memory Profiler only while the profiler is running. When you exit the profiling session, you lose the heap dump. So if you want to save it for review later, export the heap dump to an HPROF file by clicking Export capture to file , in the toolbar below the timeline. In the dialog that appears, be sure to save the file with the .hprof suffix.

You can then reopen the file in Android Studio by dragging the file into an empty editor window (or drop it in the file tab bar).

To use a different HPROF analyzer like jhat, you need to convert the HPROF file from Android format to the Java SE HPROF format. You can do so with the hprof-conv tool provided in the android_sdk/platform-tools/ directory. Run the hprof-conv command with two arguments: the original HPROF file and the location to write the converted HPROF file. For example:

hprof-conv heap-original.hprof heap-converted.hprof

Techniques for profiling your memory

While using the Memory Profiler, you should stress your app code and try forcing memory leaks. One way to provoke memory leaks in your app is to let it run for a while before inspecting the heap. Leaks might trickle up to the top of the allocations in the heap. However, the smaller the leak, the longer you need to run the app in order to see it.

You can also trigger a memory leak in one of the following ways:

Tip: You can also perform the above steps by using the monkeyrunner test framework.

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