Where does the attribute GDB_GEOMATTR_DATA originate and what purpose does it serve?

Answer

The attribute GDB_GEOMATTR_DATA, is added to the PostgreSQL database to store complex geometries such as cubic, spline, Bezier curves or other non-circular arcs. This provides a secondary shape field for storage of irregular circular geometries.

Since a feature class can have only one shape column, the storage of circular geometries must be separate, then joined to the feature class when viewed in Esri software. The concept is similar to Oracle's SDO_geometry and SQL Server Geometry spatial types. In the PostgreSQL database, these geometries are stored in the attribute named GDB_GEOMATTR_DATA.

The GDB_GEOMATTR_DATA column is added automatically to PostgreSQL feature classes using PostGIS, but should not be added to ST_Geometry feature classes (the affected table is ST_Geometry)