If you want to install or update use the yum command and got this error in Centos server:
Error: xz compression not available
Here is the solution.
This problem comes if you installed a wrong epel release on your machine. If so, then you need to remove the epel release by
yum remove epel-release
Sometimes that is not enough, you need to remove the cache as well by:
rm -rf /var/cache/yum/x86_64/6/epel
Then you can install the epel-release again
yum -y install epel-release
Hope this help you, I have solved this problem on my server.