Index usage while performance issue

Hi,

I want to ask one question if it is wrong please forgive me.

I want to load 4700000 records from source to target database, for this i am using Table input -> text file output and then Text file input -> insert/update step. i having index on my id column in source and target database and when i use insert/update step then my id column is mandatory for checking new and existing records.

when comparing id column INDEX will be useful but when it is inserting/updating then performance burden will be there... if i apply index OFF before insert/update step then comparing will be slow. am i correct ? how can i achieve performance issue on index column?.

Please tell me if my question not reach you..

select
id,
key,
--,
--,
.
.
from prd