Actually I'm bit confused as I don't know where to ask. But it is mostly related to application update from play store so asking here. Many times update size is almost equal to original installation download size. So I want to know that the application is patched with new update or new version is reinstalled?
The Google Play Store supports both full application updates and delta application updates.
A delta update is a broad term that means only changes to a package will be downloaded and the changes will be merged into the existing files inside the package. In this case, the package is the apk file that's installed on your phone. In the end, it means less data is used and sent.1
As far as I know, there is no general way to force an application update to be either a full update or a delta update. Even though Google Play Store supports both, you have to take whatever type of update that the application provides.
1What are delta updates? | Android Central