Refactoring from Oracle to postgres, Do I need to drop foreign key constraitns at postgres

Best practice is to leave constraints off while doing the full load because they can cause errors. Once you are in the change data capture phase you can safely add them to the target database. Look at the "Working with indexes, triggers, and referential integrity constraints" section in the DMS Best Practices for more detail. https://docs.aws.amazon.com/dms/latest/userguide/CHAP_BestPractices.html

DMS doesn't migrate the constraints, so you don't need to drop them in the source database. You just need to not create them in the target database until you're ready. Look at the "Converting schema" section on the same page.

Hello,

Dropping foreign key is one of the option.

But using change in parameter "session_replication_role=replica" can be used to avoid all the drop and re-create of foreign keys efforts. During data replication phase, modify this parameter and post data migration, revert it to origin.

https://docs.aws.amazon.com/dms/latest/userguide/CHAP_Target.PostgreSQL.html#CHAP_Target.PostgreSQL.ConnectionAttrib

Hope this will help

Thanks