mjhjmtu

Fedora 29 enables modular repos; now, besides the traditional fedora, updates and updates-testing repos, I get another 3 repos ending with -modular:

fedora-modular.repo
fedora.repo
fedora-updates-modular.repo
fedora-updates.repo
fedora-updates-testing-modular.repo
fedora-updates-testing.repo

my biggest question is: what is the difference when install from a traditional
repo and a modular repo?

I have briefly read this article; I understand modularity allows users to
switch between different streams of the same software (for example, node-6 to
node-8); but I think this is already possible when you downgrade and upgrade in
traditional repos; what is new here?

since I have 6 repos right now, I really want to disable some of them; should I
disable the traditional ones, or the modular ones? will they co-exist for a long
time? will one soon replace another?

The Fedora modular repo, at the moment, contains very little.

# dnf --disablerepo="*" --enablerepo=fedora-modular list available
Last metadata expiration check: 0:11:36 ago on Sat 12 Jan 2019 06:39:23 PM EST.
Available Packages
dwm.x86_64 6.1-8.module_1995+c3e93812 fedora-modular
dwm-user.x86_64 6.1-8.module_1995+c3e93812 fedora-modular
libgit2-devel.x86_64 0.27.4-1.module_2222+9bfbc8d7 fedora-modular
python-pygit2-doc.noarch 0.27.2-1.module_2222+9bfbc8d7 fedora-modular
python2-pygit2.x86_64 0.27.2-1.module_2222+9bfbc8d7 fedora-modular
stratisd.x86_64 1.0.0-1.module_2238+b7fada88 fedora-modular

If you use one of these packages, then of course you need to keep it enabled. But in F30 and future releases, much more will be added, so you will find that packages you already use are being moved to the modular repos in the future.

Also, this design is being used in RHEL 8. In RHEL, they have moved a lot of software to AppStream, which is what they are calling their modular repos. The majority of RHEL 8 packages are shipped in AppStream in the RHEL 8 beta.

[root@localhost ~]# yum --disablerepo="*" --enablerepo=rhel-8-for-x86_64-baseos-beta-rpms list available | wc -l
1070
[root@localhost ~]# yum --disablerepo="*" --enablerepo=rhel-8-for-x86_64-appstream-beta-rpms list available | wc -l
3742

All this means that you should leave these repos enabled. Note that out of those six repos, only four are enabled. The updates-testing repos are not enabled by default. You only enable these repos if you are testing an update candidate and reporting in bodhi as to whether it fixes a bug.

BTW, there's nothing inherently wrong with having a lot of repos enabled. My F29 workstation currently has 24 enabled repos all the time.