For upgrades where the starting schema version is less than 7.5.0.0, the synchronization framework is used for propagating data between the IN_DOC and NEW_DOC tables. This framework facilitates the column modifications and population and index creation of the new version of the IN_DOC table in uptime.
When the uptime steps get to the 7.4.0.3 to 7.5.0.0 portion of the upgrade it will automatically run the IN_DB_UPGRADE_SP_SYNC_SETUP_IN_DOC procedure to setup the synchronization framework for the IN_DOC table.
Note: Synchronization creates a small amount of overhead. As data
changes in the IN_DOC table, those changes are recorded and staged and must be
propogated to the new table. It is advised to delay synchronization until closer to the
downtime event.