How to rebuild RPM database on a Red Hat Enterprise Linux system?

Issue

• RPM is not working correctly, updates cannot be applied.
• How to rebuild the RPM database?
• Why does rpm command segfault when executed?
• yum update fails with rpmdb errors.
• Damaged header instance error
• rpm command terminates with "cannot open Packages database in /var/lib/rpm"
• Why does rpm or yum terminate with rpmdb: Lock table is out of available locker entries?
• Attempted to do an rpm -q on a couple of packages and got errors like this:

rpmdb: /var/lib/rpm/Packages: unexpected file type or format  
error: cannot open Packages index using db3 - Invalid argument (22)

• On doing rpm query or install, it is failing with following error:-

error: rpmdbNextIterator: skipping h#    1601 Header V4 RSA/SHA1 signature: BAD, key ID 2874ffbe

• Why "rpm -qa" command is not showing installed packages?
• rpm command hangs/hung
• rpm database got corrupted