[CentOS] Yum segmentation fault updating from 5.6 to 5.7

I've finally managed to update one of my boxes to 5.7. I did it in a 
very roundabout way, which however confirms that at least in my boxes 
there's something wrong in the way yum creates the sqlite databases.

I've basically followed the guide at 
http://wiki.centos.org/HowTos/CreateLocalMirror to create my own mirror 
of the 5.7 'os' and 'updates' directories, created the yum repository 
with 'createrepo -d' to pre-create the sqlite database and made this 
mirror accessible to the other boxes via HTTP.

I then created a /etc/yum.repos.d/Local.repo file which specifies my 
private mirror for the [base] and [updates] repositories, commented out 
everything in the /etc/yum.repos.d/CentOS-Base.repo and ran

yum clean all
yum update

Everything updated flawlessly and the box restarted normally with the 
newer kernel.

Now, this doesn't solve the original yum problem, but at least confirms 
that the creation of a corrupted sqlite database was indeed the real 
issue.

Many thanks to all the people on the list who have suggestions and 
advice, particularly to Alain Péan who pointed me in the right 
direction.

Have a nice weekend
Sebastiano Pilla