Interesting post. Curious, assuming this is used to more efficiently store user uploaded files, does Dropbox blindly apply the compression across all user files or selectively applies them (e.g. if file is already compressed like jpeg then ignore)?
To compress files for a system like Dropbox we would recommend
a) check if the file can compress with https://github.com/dropbox/lepton . Lepton has some new flags that can help it compress a wider range of files, so it's not just limited to pure JPEG files any longer.
b) then compress it with zlib -6 to get an idea of how compressible the data is.
c) if the data compresses by at least a percent with zlib, it's likely to do significantly better with more advanced compression like DivANS. About 1/3 of files in Dropbox fall into that >1% category but aren't compatible with Lepton. For those compressible files, DivANS gets 12.08% savings over zlib with the settings we chose in the blog post. Brotli, in contrast, gets 9.64% savings over zlib on that same data.