The following warning appears after Plesk pre-upgrade check:
WARNING: You have a mixed set of 'php' and 'php53' packages installed. Installation or upgrade may fail or produce unexpected results. To resolve this issue run "sed -i.bak -e '/^\s*skip-bdb\s*$/d' /etc/my.cnf ; yum update 'php*' 'mysql*'".
Some PHP packages are installed from different repositories.
Warning can be safely ignored.