you don’t like the performance?

This is one time work or your goal is to insert 50M records every time? Inserting 50m records without committing, is not the best idea you can do with Redo.. Also on which table you have PK? Table1 or Table2? What is the point of having PK on varchar data type column? This kind of a solution might have performance issues, because indexing and lookup operations on varchar columns are generally slower than on numeric columns because string comparison + validation overhead and in long term it will cost you more storage…

So I would recommend to commit after every 10K - 50K records are inserted… Maybe this will help.