We have been distributing our app with bundled resources included in the application package. In our latest release, we updated a portion of those bundled resources for the first time. However, the delta download mechanism did not function properly, resulting in users being forced to re-download a significantly large amount of data.
The versions we have released so far are as follows:
- 1.0.0: Initial release
- 1.0.1: Bug fixes only. The executable was updated, but no changes were made to the resources.
- 1.0.2: Same as above — only the executable was updated; no changes to resources.
- 1.1.0: Feature update. Includes changes to both the executable and part of the bundled resources.
🔽 The IPA file sizes for each version are as follows:
- 1.0.0: 2.2 GB
- 1.0.1: 2.2 GB
- 1.0.2: 2.1 GB
- 1.1.0: 2.36 GB
We had no reliable way to evaluate the actual download size at update time, so the precise size is unclear. However, updates from version 1.0.0 to 1.0.2 consistently completed within 30 seconds, even over a mobile network.
In contrast, when we released version 1.1.0, the situation changed significantly: a full download of 2.4 GB was triggered, even though only part of the resources had actually been updated. It appears that almost all bundled resources were re-downloaded regardless of whether they had changed. (The attached image shows the actual download confirmation dialog displayed to users during this update.)
Based on the xcarchive used for App Store submission, we compared file differences and summarized them as follows:
- Updated files: 311 files / 513 MB
- Deleted files: 6 files / 12.6 KB (excluded from total since they are not redistributed)
- Added files: 417 files / 166 MB
- Total: 734 files / 679 MB
(Comparison was performed under Unity-iPhone.xcarchive/Products)
As described in the following Apple documentation, we expected only the ~679 MB delta to be delivered to users: 🔗 https://developer.apple.com/documentation/xcode/doing-advanced-optimization-to-further-reduce-your-app-s-size#Reduce-the-size-of-app-updates
If there are any additional build settings or techniques we should consider to ensure that delta updates are correctly detected and applied, we would greatly appreciate your guidance.
