What happen before and after user Commit Fire in Oracle

The COMMIT statement ends a transaction successfully. All changes made by all SQL statements since
the transaction began are recorded permanently in the database. Before the COMMIT statement is
issued, the changes may not be visible to other transactions.
You can commit a transaction by using either of the following statements, which make the
changes permanent:
SQL> COMMIT;
3 things that happen Before Commit:
1. Oracle generates undo records in the undo segment buffers in the SGA. As you know, the
undo records contain the old values of the updated and deleted table rows.
2. Oracle generates redo log entries in the redo log buffers in the SGA.
3. Oracle modifies the database buffers in the SGA.
3 things that happen AFTER Commit:
1. The transaction tables in the redo records are tagged with the unique system change number
(SCN) of the committed transaction.
2. The log writer writes the redo log information for the transaction from the redo log buffer to
the redo log files on disk, along with the transaction’s SCN. This is the point at which a commit
is considered complete in Oracle.
3. Any locks that Oracle holds are released, and Oracle marks the transaction as complete.