OQGRAPH cannot be installed on CentOS 6.5/RHEL 6.5
Try to install MariaDB-oqgraph-engine.x86_64. See it fail because it requires libJudy, which does not exist in CentOS/RHEL 6. It works on Fedora, and I notice there are "EPEL" packages (which means you need to enable yet another repository for this to work). But out of the box, this is a problem.