It appears that the RPM database needs rebuilding if a yum process is killed
prematurely, since it probably had the RPM db open and now it’s in an inconsistent
state.

The steps :

• Kill all yum and rpm processes.
• rm -f /var/lib/rpm/__db*
• rpm –rebuilddb

  (add -vv if you want to see what it’s doing)

• Retry
  yum update

  .