Hello per my discussion with support team (Ticket number: #216893) derived mapping does not have identifier functionality which is a huge miss for customer that are working through data issues.
USE CASE: I am creating relationship and i do not have company GSID field available within data set up and therefore i am using derived mapping to map SFDC field to Company GSID see below example of derived mapping configuration:

Per my understanding of the relationship object Company ID is required

So then why is it not auto chosen as an Identifier from the derived mapping? Per my conversation with support they are saying this is the expected behavior. This is a huge miss on Gainsight part to have derived mapping function as a key feature in connector 2.0, rules engine, real-time, etc.
PROBLEM STATEMENT: When derived mapping is used to upsert relationship values this field is getting updated rather than being used to determine update versus creation. We have 10k relationship move into once company due to this issue.
ASK: Can you please enhance this feature all of the features so that we can used derived mapping as an identifier to create uniqueness within our records.
Thank you team for your attention.
Best Regards,
Darshana Shah