Re:Why are tar.xz files 15x smaller when using Python's tar ...
by yongjik on Monday March 15, 2021 @05:33PM
(#26469417)
Well, I did say "about 37% if you consider .gz as baseline", but I agree that it could have been worded better.
The problem is what you are measuring. If you have to compress a 100MB file, and algorithm A/B/C/D compress it to 10/9/1/0.9MB, respectively, then we can argue that "B is 10% better than A" (because the file is 10% smaller) and also "D is 10% better than C" (same).
However, moving from A to B saves us 1MB for this file. Moving from C to D only saves us 0.1MB. So depending on how you look at it, you could also argue that the difference between C and D is really only 0.1% (of the original file size). It may not be what you want (for a particular situation), but it's not wrong.
The problem is what you are measuring. If you have to compress a 100MB file, and algorithm A/B/C/D compress it to 10/9/1/0.9MB, respectively, then we can argue that "B is 10% better than A" (because the file is 10% smaller) and also "D is 10% better than C" (same).
However, moving from A to B saves us 1MB for this file. Moving from C to D only saves us 0.1MB. So depending on how you look at it, you could also argue that the difference between C and D is really only 0.1% (of the original file size). It may not be what you want (for a particular situation), but it's not wrong.