Description of problem: yum (after the dnf fork) has added support for parallel downloads and other enhancements, bug fixes. merge those changes.
While looking into this, you might want to incorporate some improvements from http://repos.fedorapeople.org/repos/hedayat/yum-fast-downloader/ It downloads aggressively from multiple mirrors by using aria2 as a backend
There was a considerable backlash against using too many connections (downloading 2 files from the same mirror in parallel, or downloading 1 file from 2+ mirrors with range request). People that run the mirrors were seriously concerned (and the parallel downloading code in Yum is not aggressive by any means) http://lists.fedoraproject.org/pipermail/devel/2012-May/167122.html
From the thread, there isn't really much of a backlash. There are some mirror admins who were concerned that yum is using more than one connection to the same mirror but yum fast downloader distributes this load. Either way, yes, dnf developer would need to talk to the mirror admins and figure out what is the optimal way to handle this.
The DNF version in F19 and beyond uses librepo for the repodata and package download backend. By default librepo downloads different metadata files per repo in parallel. It currently however does not download repositories in parallel, nor packages in parallel. Careful extension of librepo API will have to happen first, leaving this open until then.
(In reply to Ales Kozumplik from comment #4) > Careful extension of librepo API will have to happen first, leaving this > open until then. Tomas, can librepo already do parallel download of packages?
Moving over to Zdenek who implemented parallel downloads in Yum and is in touch with tmlcoch about how to do this with librepo.
Librepo since 1.0.0 supports parallel downloads out-of-box.
dnf-0.4.2-1.gitc1716d7.fc20 has been submitted as an update for Fedora 20. https://admin.fedoraproject.org/updates/dnf-0.4.2-1.gitc1716d7.fc20
Package dnf-0.4.2-1.gitc1716d7.fc20, librepo-1.2.0-1.fc20, hawkey-0.4.2-1.git4c51f65.fc20: * should fix your issue, * was pushed to the Fedora 20 testing repository, * should be available at your local mirror within two days. Update it with: # su -c 'yum update --enablerepo=updates-testing dnf-0.4.2-1.gitc1716d7.fc20 librepo-1.2.0-1.fc20 hawkey-0.4.2-1.git4c51f65.fc20' as soon as you are able to. Please go to the following url: https://admin.fedoraproject.org/updates/FEDORA-2013-18123/librepo-1.2.0-1.fc20,hawkey-0.4.2-1.git4c51f65.fc20,dnf-0.4.2-1.gitc1716d7.fc20 then log in and leave karma (feedback).
dnf-0.4.2-1.gitc1716d7.fc20, librepo-1.2.0-1.fc20, hawkey-0.4.2-1.git4c51f65.fc20 has been pushed to the Fedora 20 stable repository. If problems still persist, please make note of it in this bug report.