ovs-vswitchd.conf.db - Open_vSwitch database schema
       A database with this schema holds the configuration for one Open
       vSwitch daemon. The top-level configuration for the daemon is the
       Open_vSwitch table, which must have exactly one record. Records
       in other tables are significant only when they can be reached
       directly or indirectly from the Open_vSwitch table. Records that
       are not reachable from the Open_vSwitch table are automatically
       deleted from the database, except for records in a few
       distinguished ``root set'' tables.
   Common Columns
       Most tables contain two special columns, named other_config and
       external_ids. These columns have the same form and purpose each
       place that they appear, so we describe them here to save space
       later.
              other_config: map of string-string pairs
                     Key-value pairs for configuring rarely used
                     features. Supported keys, along with the forms
                     taken by their values, are documented individually
                     for each table.
                     A few tables do not have other_config columns
                     because no key-value pairs have yet been defined
                     for them.
              external_ids: map of string-string pairs
                     Key-value pairs for use by external frameworks that
                     integrate with Open vSwitch, rather than by Open
                     vSwitch itself. System integrators should either
                     use the Open vSwitch development mailing list to
                     coordinate on common key-value definitions, or
                     choose key names that are likely to be unique. In
                     some cases, where key-value pairs have been defined
                     that are likely to be widely useful, they are
                     documented individually for each table.