Rawhide is running with xz repodata enabled, but dnf is still pulling some of the old .gz repodata. In particular dnf uses: primary.xml.gz filelists.xml.gz while there is primary.sqlite.xz and filelists.sqlite.xz available. The primary sqlite is actually larger than the primary xml, but the filelists sqlite is a good deal smaller than the xml. It might make sense to adjust on the createrepo side to xz compress the xml files, but I don't know what that might break compatibility wise.
I'm looking at https://ftp.fau.de/fedora/linux/releases/20/Everything/x86_64/os/repodata/ and .filelist.xml.gz is 26M while filelist.sqlite.bz2 is is 27MB. In rawhide where .xz is used there is some saved bandwidth but it is only 12%: https://ftp.fau.de/fedora/linux/development/rawhide/x86_64/os/repodata/ That doesn't buy us enough to justify more complex handling and additional processing time from .sqlite to the libsolv format. We're moving away from sqlite, perhaps towards distributing the libsolv MD files directly.
ok. Perhaps however it's worth getting createrepo to make .xz copies of the xml files?