Projections for enforced constraints

To enforce primary key and unique constraints, Vertica creates special constraint enforcement projections that it uses to validate new and updated data. If you add a constraint on an empty table, Vertica creates a constraint enforcement projection for that table only when data is added to it. If you add a primary key or unique constraint to a populated table and enable enforcement, Vertica chooses an existing projection to enforce the constraint, if one exists. Otherwise, Vertica creates a projection for that constraint. If a constraint violation occurs, Vertica rolls back the statement and any projection it created for the constraint.

If you drop an enforced primary key or unique constraint, Vertica automatically drops the projection associated with that constraint. You can also explicitly drop constraint projections with DROP PROJECTION. If the statement omits CASCADE, Vertica issues a warning about dropping this projection for an enabled constraint; otherwise, it silently drops the projection. In either case, the next time Vertica needs to enforce this constraint, it recreates the projection. Depending on the amount of data in the anchor table, creating the projection can incur significant overhead.

You can query system table PROJECTIONS on Boolean column IS_KEY_CONSTRAINT_PROJECTION to obtain constraint-specific projections.