How to implement partial transaction rollback (not full, but up to a certain point)?.

Partial rollback of a transaction is implemented using savepoints. A savepoint allows you to set a control point within a transaction to which you can roll back without canceling the entire transaction.

Example in SQL (PostgreSQL):

BEGIN;
-- operation 1
SAVEPOINT sp1;
-- operation 2
-- if you need to rollback only to sp1
ROLLBACK TO SAVEPOINT sp1;
-- continue the transaction
COMMIT;

Thus, you can rollback changes only after the savepoint, preserving previous changes within a single transaction.