When using OpenVAS in larger environments (e.g. lots of tasks and/or lots of slaves) you may have noticed the manager controlling all the slaves/scans can get sluggish or unresponsive at times. In my experience it is often due to the different processes waiting for an exclusive lock on the sqlite database. Fortunately OpenVAS 8 and above also supports using PostgreSQL as a database backend instead of sqlite. I think OpenVAS 7 also had support built-in, but it was still considered experimental.
Documentation on how to use PostgreSQL as the backend is in the OpenVAS svn repository. In a nutshell it is mainly adding -DBACKEND=POSTGRESQL to your cmake when you compile the manager (my cmake line is cmake -DCMAKE_INSTALL_PREFIX=/ -DCMAKE_BUILD_TYPE=Release -DBACKEND=POSTGRESQL ..). I generally only compile the master with PostgreSQL support and leave the slaves to use sqlite (since they don’t have as many concurrent accesses to their database). The documentation also steps you through the permissions you need to set up in PostgreSQL so it can be used by OpenVAS. Don’t forget to make the system aware of your OpenVAS libraries, in my case since I install OpenVAS to / I put /lib64/ in my /etc/ld.so.conf.d/openvas.conf file and then execute ldconfig.
One issue you may run into is migrating data from sqlite to PostgreSQL. There is a migration script in svn that can migrate the data, but it only works for a few older database versions. I assume OpenVAS 9 will contain an updated version of the script when it is released, but until then I wrote a script that uses the OMP protocol to export/store/import some of the settings. Since it only uses OMP to communicate with the master it is backend agnostic. You can use it to export the sqlite data and import it back into a manger using the PostgreSQL backend. It also means that it can only access data you can export via OMP (so no credential passwords/keys). The script will keep references intact (which tasks uses which target/schedule/…). The list of what it exactly imports/exports is on the github page: github.com/ryanschulze/openvas-tools