ovsdb-idl: compound indexes design document

ovsdb-idl: compound indexes design document

In the work made in our projects, it was found the need to have a faster
access to the rows contained in tables in the replica, as well to have
the possibility to loop over a subset of rows that meet some specified
criteria.
Those needs lead us to design and implement a functionality that
satisfies those requirements, so an implementation of special indexes were
done.
In order to keep the OVSDB server implementation unmodified and avoid
extra load of processing, the indexes are created as part of the IDL.
The indexes are created as part of the initialization of the replica request
and are maintained automatically when there are changes in the replica.

This document explains the design rationale of the compound indexes feature.

Signed-off-by: Javier Albornoz <javier.albornoz@hpe.com>
Signed-off-by: Esteban Rodriguez Betancourt <estebarb@hpe.com>
Signed-off-by: Jorge Arturo Sauma Vargas <jorge.sauma@hpe.com>
Co-authored-by: Javier Albornoz <javier.albornoz@hpe.com>
Co-authored-by: Esteban Rodriguez Betancourt <estebarb@hpe.com>
Co-authored-by: Jorge Arturo Sauma Vargas <jorge.sauma@hpe.com>
Co-aughored-by: Lance Richardson <lrichard@redhat.com>
Signed-off-by: Lance Richardson <lrichard@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>