By default, Polaris will be using in-memory backend as defined in https://github.com/polaris-catalog/polaris/blob/main/polaris-server.yml#L90. However, there is no documentation on what are the allowed values as well as how to use eclipselink (https://github.com/polaris-catalog/polaris/tree/main/extension/persistence/eclipselink) to switch to non-default backend.