I recently read about that Google is using File-by-File Patching and another one algorithm BsDiff - Delta update which patches apk files and gives only update sized apk to download from Play Store.
I went through below blogs and links:
2) https://github.com/andrewhayden/archive-patcher/blob/master/README.md for "File-by-File Patching"
3) https://android-developers.googleblog.com/2016/07/improvements-for-smaller-app-downloads.html for "BsDiff" patching
I installed BsDiff on my Linux and applied it on old and new apk but it remains the same size of the app and also while I update it on Play Store, it shows full size as at the time of install.
Also, I downloaded "File-by-File Patching" code and made apk through it and updated it on Play Store but the same, no reduced size of apk.
So, If anybody who has done this or know about this, Please give your answer so I can make my app update of reduced size app update on Play Store.
You don't need to do anything to trigger these APK size reductions for updates. You definitely don't need to download BS Diff or the patching code. Play will do this automatically for you. However some optimizations are applied on demand depending on how popular an app is. So if your app is not very popular it might take a little while to see the advantages.
If you want Google to be able to apply as many optimizations as possible, you should opt in to Google Play App Signing if you haven't already. This gives Google Play the most ability to optimize app updates, and while it doesn't affect these optimizations right now it may in future.