Delta Patches seem way too big

[justtoask]

I needed to create a delta patch for the data.hst file for Rayman 3, however it weighed 535 MB when done through RCP, for comparison when I did it with any generic patch tool like delta patcher its size drops to 28 MB. Why is that?

[RayCarrot]

What and how did you replace in the .hst file?
It seems the file itself is around 500 mb, so if you changed the structure of the file then that could very well cause the delta patch to be just as big. That's because the RCP delta patches aren't compressed due to the mods themselves being compressed instead. They also only check for modified bytes on the same addresses, meaning that if the data shifts then that is all going to be seen as modified data. This is to allow multiple delta patches from different mods to be combined without any conflicts.
Because of this delta patches should only really be used for files where data is in a fixed address, such as exe files. Otherwise it's better just doing it as a file replacement or if there's a module in RCP to support it, like how the UbiArt games have a localization replacement module to replace individual localized strings.

[justtoask]

I didn't replace anything, I just wanted to create a proper Polish translation patch to use with RCP. I think atm the delta patches should just use xdelta for anything other than exe because there's little interest in repacking the audio files and it reduces the size heavily.

[RayCarrot]

I'll consider it. The problem is more that when using xdelta then multiple mods can't be combined, and it also requires that you have the same version of the game that the delta patch was made from. But I agree that having modes be several hundred megabytes large isn't ideal either, so perhaps this should be added as an option.