Why bulk loading a Vertica database table does not load all lines?
Try option ABORT ON ERROR - will output a reason for rejection.

COPY 'table name' FROM '/path/to/data.txt' DIRECT RECORD TERMINATOR ',' ABORT ON ERROR 


Check rejected and exception files or define it in COPY: 

COPY 'table name' FROM '/path/to/data.txt' DIRECT RECORD TERMINATOR ',' REJECTED DATA 'path' EXCEPTIONS 'path' 


https://community.vertica.com/vertica/topics/bulk_loading

(Original URL is dead; you can try this one instead)