The plugin yum-fastestmirror is really simple in concept. It simply maintains a text file with times that YUM accumulates about each mirror and then when YUM is asked to download packages, it uses the server that's shown as the fastest for the duration of the download.
The times are stored in this location:
$ locate timedhosts.txt
If we inspect this file we'll come to find it's just hostnames with times next to each. Here we're sorting it from fastest to slowest:
$ sort -k2,2 /var/cache/yum/x86_64/7/timedhosts.txt
Now when we inquire about a specific package's location if we were to download it using
$ $ repoquery --location java-1.8.0-openjdk
The yum-fastestmirror plugin also has its own config file:
$ more /etc/yum/pluginconf.d/fastestmirror.conf
always_print_best_host = true
# Relative paths are relative to the cachedir (and so works for users as well
# as root).
Through this file we can instruct the plugin to whitelist & blacklist specific mirrors that have either presented us with issues in the past or we've deemed unacceptable for whatever reasons.