ADF Provides extension to standard Java Preferences API and is maintained in MDS Repository.
You can reference following Javadoc and Blog:
oracle.mds.exception.ReadOnlyStoreException: MDS-01273: The operation on the resource /oracle/adf/share/prefs/data/preferences.xml failed because source metadata store mapped to the namespace / DEFAULT is read only.
<persistence-config>
<metadata-namespaces>
<namespace path=”/oracle/adf/share/prefs” metadata-store-usage=”MAR_TargetRepos”/>
<namespace path=”/persdef” metadata-store-usage=”MAR_TargetRepos”/>
</metadata-namespaces>
<metadata-store-usages>
<metadata-store-usage id=”MAR_TargetRepos” deploy-target=”true” default-cust-store=”true”>
</metadata-store-usage>
</metadata-store-usages>
</persistence-config>