Is Vertica's COPY atomic?
Vertica supports ANSI SQL-92 isolation levels with standard ACID properties. If a COPY is terminated, interrupted, or an error occurs, it will be rolled back.

By default, HP Vertica uses the READ COMMITTED isolation level.
The COPY command automatically commits itself and any current transaction (except when loading temporary tables). HP recommends that you COMMIT or ROLLBACK the current transaction before you use COPY. Please note that DDL statements are autocommitted.

Documentation