[migration/3.21.0] performance and reliability fixes - use EXCEPT instead of NOT IN, seems to improve performance dramatically on postgresql - delete rows from cw_<etype> tables whose eid is unknown - deal with missing/dangling required inline relations (by deleting the subject entities) instead of asserting - fix/improve print statements - don't ask for confirmation before running pure select queries

Additional services
===================

In this chapter, we introduce services crossing the *web -
repository - administration* organisation of the first parts of the
CubicWeb book. Those services can be either proper services (like the
undo functionality) or mere *topical cross-sections* across CubicWeb.

.. toctree::
   :maxdepth: 2

   undo