Optimal way of loading, registering, indexing and querying a huge XMLDB
Wouter got, hopefully, useful answers here:

https://community.oracle.com/message/12608939

That said, being the Oracle ACE Director for this technology. Oracle XMLDB functionality is nowadays so interwoven with the Oracle database that this is an MANDATORY (install) functionality for Oracle 12c and onwards. It is the basis for much in the database like ACL security, database security, Database Vault, Oracle APEX, Multitenent functionality, import and export, DBMS_packages like DBMS_METADATA, Oracle performance implementations (AWR XMLtype columns etc etc), DBA/Developer tools like DB Express...

XML is (alas?) everywhere nowadays. To give one example, you using it now (that is if you use a mobile phone...)