800000 is not a huge number but still larger than, say, 3000-4000 rows in oracle. Please follow the pattern of having a stage table in between your ssis and the actual target table.

So that way,

First, have everything in a stage table.

Then write a stored procedure which will do a mismatch between the stage and the target table and update / insert accordingly. Even there, might i suggest, don't use a cursor to loop through the rows, use the MERGE command.