it often happened some rows with format issue, data type issue rejected by copy command while try load it by copy command. the query return succeed but some of data rejected.
To do troubleshooting
COPY large_tbl FROM :file1 ON site01,
:file2 ON site01,
:file3 ON site02,
:file4 ON site02
DELIMITER '|'
REJECTED DATA :reject_s1 ON site01, :reject_s2 ON site02
EXCEPTIONS :except_s1 ON site01, :except_s2 ON site02;