Why does an Android App lag?

  • Amit Shekhar
    Amit Shekhar
    Published on
Why does an Android App lag?

I am Amit Shekhar, a mentor helping developers in getting high-paying tech jobs.

In this blog, we will learn why an Android App lags. I believe that every Android Developer should know the reason for the low performance of the Android app.

I will start with the following statement:

Garbage Collector: The TAX on Android App Performance

The main reason for the Android App lag or for the low performance of the Android app is that it runs GC very frequently.

Simple in one line: The time for which GC is running the actual app is not running.

Basically, when the Android App runs, it allocates many objects on the basis of your code, and when the objects are no longer referred to, the system calls GC when there is memory pressure to deallocate those objects.

So, if the object allocation and deallocation occur on the regular basis, it means that the GC will run on a regular basis to release memory.

Here, the important point is that the time for which the GC runs, your app does not run for that time. So, it seems that the app is lagging. And hence, a bad experience for the user of the application. Let's understand it deeply.

The Android app updates its UI every 16ms (considering 60FPS -> 1000ms/60 = 16.67ms ~ 16ms) for smooth UI rendering.

Frame per second (FPS) is the measurement of the number of frames that appear within a second.

Android frame update

So, if the GC runs for more time, the app will be unable to update UI and it will skip a few frames, so it will seem that the app is lagging. That is one of the reasons for the app lag.

Another reason is that the app is doing too much on the main thread. For example, at that time if any method/task is taking more time than 16ms, the app will be unable to update UI, which means lag will be there in the app for that time.

Basically, the system tries to redraw the UI every 16ms, and what if our task on the main thread takes more than 16ms? For example, if our task takes 26ms. The system tries to update the UI, but it wasn't ready. In that case, it will not refresh anything. And, that caused the UI to be refreshed after 32ms instead of 16ms. Ultimately, there will be a frame drop.

Android frame update delayed

So, due to the frame drop, the user finds the app laggy.

Even if there is one dropped frame, the animation will not be smooth. The user will find it laggy.

Now, we have understood the two most important reasons because of why the Android Apps lag which are as follows:

  • GC running frequently
  • Doing too much work on the main thread

In order to fix this lag issue, we need to focus on the following:

  • Reduce GC running time
  • Do not do too much on the main thread

That's it for now.


Amit Shekhar

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