Improvements for smaller app downloads on Google Play

Posted by Anthony Morris, SWE Google Play and Andrew Hayden, software engineer

Google Play continues to grow rapidly, as Android users installed over 65
billion apps in the last year from the Google Play Store. We’re also seeing
developers move to update their apps more frequently to push great new content,
patch security vulnerabilities, and iterate quickly on user feedback.

However, many users are sensitive to the amount of data they use, especially if
they are not on Wi-Fi. Google Play is investing in improvements to reduce the
data that needs to be transferred for app installs and updates, while making
data cost more transparent to users.

Read on to understand the updates and learn some tips for ways to optimize the
size of your APK.

New Delta algorithm to reduce the size of app updates

For approximately 98% of app updates from the Play Store, only changes
(deltas) to APK files are downloaded and merged with the existing
files, reducing the size of updates. Google Play has used delta algorithms since 2012, and we recently rolled out an additional delta algorithm, href="http://www.daemonology.net/bsdiff/">bsdiff href="http://www.daemonology.net/bsdiff/">(created by Colin Percivalid="fnref1">1href="http://www.daemonology.net/bsdiff/">), that our experimentation shows
can reduce delta size by up to 50% or more compared to the previous algorithm
for some APKs. Bsdiff is
specifically targeted to produce more efficient deltas of native libraries by
taking advantage of the specific ways in which compiled native code changes
between versions. To be most effective, native libraries should be stored
uncompressed (compression interferes with delta algorithms).

An example from Chrome:

Patch Description	Previous patch size	Bsdiff Size
M46 to M47 major update	22.8 MB	12.9 MB
M47 minor update	15.3 MB	3.6 MB

Apps that don’t have uncompressed native libraries can see a 5% decrease in size
on average, compared to the previous delta algorithm.

Applying the delta algorithm to APK Expansion Files to further
reduce update size

APK Expansion Files allow you to include additional large files up to 2GB in
size (e.g. high resolution graphics or media files) with your app, which is
especially popular with games. We have recently expanded our delta and
compression algorithms to apply to these APK Expansion Files in addition to
APKs, reducing the download size of initial installs by 12%, and updates by 65%
on average. APK Expansion file patches use the href="http://xdelta.org/">xdelta algorithm.

Clearer size information in the Play Store

Alongside the improvements to reduce download size, we also made information
displayed about data used and download sizes in the Play Store clearer. You can
now see actual download sizes, not the APK file size, in the Play Store. If you
already have an app, you will only see the update size. These changes are
rolling out now.

---

1. 
   

   
   Colin Percival, Naive differences of executable code,
   http://www.daemonology.net/bsdiff/, 2003. ↩
   

Example 1: Showing new “Download size” of APK

Example 2: Showing new “Update size” of APK

Tips to reduce your download sizes

1. Optimize for the right size measurements: Users care about download size (i.e. how many bytes are transferred when installing/updating an app), and they care about disk size (i.e. how much space the app takes up on disk). It’s important to note that neither of these are the same as the original APK file size nor necessarily correlated.

Chrome example:

	Compressed Native Library	Uncompressed Native Library
APK Size	39MB	52MB (+25%)
Download size (install)	29MB	29MB (no change)
Download size (update)	29MB	21MB (-29%)
Disk size	71MB	52MB (-26%)

Chrome found that initial download size remained the same by not compressing the native library in their APK, while the APK size increased, because Google Play already performs compression for downloads. They also found that the update size decreased, as deltas are more effective with uncompressed files, and disk size decreased as you no longer need an compressed copy of the native library. However, please note, native libraries should only be uncompressed when the minimum SDK version for an APK is 23 (Marshmallow) or later.

2. Reduce your APK size: Remove unnecessary data from the APK like unused resources and code.

3. Optimize parts of your APK to make them smaller: Using more efficient file formats, for example by using WebP instead of JPEG, or by using Proguard to remove unused code.

href="https://medium.com/google-developers/smallerapk-part-1-anatomy-of-an-apk-da83c25e7003#.jgy8wuni9">Read
more about reducing APK sizes and watch the I/O 2016 session href="https://www.youtube.com/watch?v=xctGIB81D2w">‘Putting Your App on a
Diet’ to learn from
Wojtek Kaliciński, about how to reduce the size of your APK.