Posted by the Google and Facebook teams. Authored by Kateryna Semenova from the Google Android team and Tim Trueman, Steven Harris, Subramanian Ramaswamy from the Facebook team.
Improving app startup time is not a trivial task and requires a deep understanding of things that affect it. This year, the Google Android team and the Facebook app team have been working together on metrics and sharing approaches to improve app startup. Google Android’s public documentation has a lot of information on app startup optimization. In addition to that we want to share how it applies to the Facebook app and what helped them to improve app startup.
There are now more than 2.9 billion people using Facebook every month. Facebook helps give people the power to build community and bring the world closer together. It is a place for people to share life’s moments, discover and discuss what’s happening, connect and nurture relationships, and help work together to build economic opportunity.
Facebook app developers are committed to ensure that people have the best possible experience and that the app works seamlessly on every device, in any country, and within different network conditions. Working together, the Google Android team and Facebook team aligned on metrics definition for app startup and best practices and shared them in this article.
Start by measuring your startup times. This will let you know how good your user’s startup experience is, track any regressions, as well as how much to invest on improving it. At the end of the day, your startup times need to be tied to user satisfaction or engagement or user-base growth in order to prioritize your investments.
Android defines two metrics to measure app startup times: Time-To-Full-Display (TTFD) and Time-To-Initial-Display (TTID). While you can further split it into cold/warm startup times, this post will not disambiguate between them - Facebook's approach is to measure and optimize the startup time that’s experienced across all users interacting with the app (some of them will be cold, some warm).
TTFD captures the time when your app has completed rendering and is ready for user interaction and consumption, perhaps including content from disk or the network. This can take a while on slow networks and can depend on what surface your users land on. Thus, it may also be helpful to show something right away and let users see progress is still happening, which brings us to TTID…
TTID captures the time for your app to draw its background, navigation, any fast-loading local content, placeholders for slower local content or content coming from the network. TTID should be when users can navigate around and get to where they want to go.
Your users are coming to your app for content that might take a while to load, and you want to deliver that content to them as quickly as you can.
Facebook app developers focus on a metric based on Time To Full Display (TTFD), including all content and images, because that represents the full experience of what users came to the app for. If a network call for content or an image takes a long time or fails, developers want to know so that they can improve the entire start to finish startup experience.
Facebook’s startup metric is the percentage of app starts that they consider “bad,” which is any start that either has a TTFD longer than 2.5 seconds OR any part of startup that is unsuccessful (e.g. an image fails to load or the app crashes). Facebook focuses on driving this percentage of bad starts down either by improving successful starts that take longer than 2.5 seconds, or by fixing issues causing unsuccessful starts. 2.5 seconds was chosen based on research that showed this was meaningful to Facebook users (this also matches the Largest Contentful Paint (LCP) metric in the Web Vitals recommendations for web sites).
Including the full experience, especially of any network calls to fetch recent content, can make your TTFD startup metrics seem really slow compared to TTID. This is actually a good thing! It represents the real experience people have with your app. Improvements you make to this may drive increased usage and perception of your app’s performance for your users like it has at Facebook.
Measuring TTFD can be tricky depending on your app. If it’s too hard, it’s fine to start with Time To Initial Display (TTID). That may miss the performance of loading some of your content if you have placeholders or images, but it’s good to start somewhere even if it’s just a subset of what your users see interacting with your app every day.
In Android 4.4 (API level 19) and higher, logcat provides a “Displayed” value capturing the time elapsed between launching the process and the completion of drawing the first frame of the corresponding activity on the screen.
The reported log line looks similar to the following example:
ActivityManager: Displayed com.android.myexample/.StartupTiming: +3s534ms
To instrument TTFD, call reportFullyDrawn() in your Activity after all your content is on screen. Be sure to include any content that replaces placeholders, as well as any images you render (be sure to count when the image itself is displayed, not just its placeholder). Once you instrument calling reportFullyDrawn(), you can see it in logcat:
ActivityManager: Fully drawn {package}/.MainActivity: +1s54ms
Facebook app developers have been optimizing the app for billions of users across a multitude of devices, platforms and countries for many years. This section shares some of the key lessons that Facebook app developers applied to optimize their app startup.
Google Android team’s recommendations to measure and optimize app startup are available in the public docs: App startup time. This section summarizes some of the key points that ties into Facebook’s recommendations above that all Android app developers should consider.
This article captures some key measures of startup and best practices to improve startup experience that helps drive user engagement and adoption for the Facebook Android app. It also shares metrics, libraries and tools recommended by the Google Android team. Any Android app stands to benefit from applying some of the strategies described in the document. Measure and make your app startup delightful and fast for your users!
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