You can now download zchunk metadata in Rawhide

It’s been a long push, but the downloading of zchunk metadata is now fully functional in Rawhide. Included in the next Rawhide push is libdnf-0.26.0-2.fc30, which, when installed, will automatically download zchunk metadata wherever it’s available.

It’s been a year since I first started working on zchunk, and I’m excited that we’ve finally managed to get it fully integrated into Fedora’s metadata. I’d like to take the opportunity to express my appreciation to Daniel Mach, Jaroslav Mracek and the rest of the DNF team for reviewing and merging my (quite invasive) patches, Michael Schroeder for extensive critiques and improvements on the zchunk format, Igor Gnatenko for help early on, and, finally, Neal Gompa for working behind the scenes to keep things moving.


David Anderson
Saturday, Feb 23, 2019

Hi Jonathan,

This sounds exciting and should enhance the existing savings from deltarpm. However, for a long time, over a long period of time on several machines, I find that those existing savings are almost zero. So, just now I updated a Fedora 29 machine I updated 613 packages at a total of 1.2GB, and saved all of 500KB when doing so:

Total 387 kB/s | 1.2 GB 54:55
Delta RPMs a réduit la taille des mises à jour de 1246.4 Mio à 1245.9 Mio (0.1% économisés)

What could be going wrong?

Jonathan Dieter
Sunday, Feb 24, 2019

Hey David, you’ve run into a known bug, but one that probably isn’t documented anywhere. The problem is that the compose process has changed, and in the process, lost the ability to save old deltarpms. So we generate deltarpms for any new packages in the latest compose, but then throw them away when the next compose happens. This means that you’ll only ever get deltarpms for the latest compose. :(

David Anderson
Tuesday, Feb 26, 2019

Thanks for the explanation! Has this been going on a looonng time, or is that just my subjective imagination? It does feel like a long time since deltarpms were being useful. I tend to pay attention as I’m often on connections where it makes a difference.

Jonathan Dieter
Tuesday, Feb 26, 2019

It’s been going on a while. I was looking for an email thread that I started on the subject, but I can’t find it. I want to say that it’s been happening for at least a year, but I could be wrong. And I do feel your pain. My slow internet was the reason I pushed getting deltarpms into Fedora in the first place.