On the page: https://doc.ez.no/eZ-Publish/Technical-manual/5.x/Features/Clustering/Cluster-File-Handlers

There is chapter on "Supported database". It is not up to date as it should link on the requirement page of the given version, for example on 5.2: https://doc.ez.no/display/EZP/Requirements+5.2
Where we can see that pgsql is not supported.