Sometimes RPM databases become corrupt. You will no longer be able to install/upgrade/remove programs using YUM or RPM command. Even RPM query simply gets hung. 

This is the case when you need to repair RPM databases. To repair do the following:

cp -rp /var/lib/rpm{,`data +%F`.bk}

This command is to take a backup of  ‘ /var/lib/rpm‘ directory

rm -f /var/lib/rpm/__db*

This command clears the RPM database. Then enter the following command

rpm -vv –rebuilddb

This command rebuild database in verbose mode so that you see the process. Now your RPM database is perfect.
You can just check following command to confirm this.

rpm -qa