Does canceling update operation perform automatic rollback
If you do that, the statement is rolled back, not the transaction. Below I hit Ctrl+C after starting the UPDATE.

SQL&gt; drop table t1 purge;

Table dropped.

SQL&gt; create table t1 as select * from dba_objects;

Table created.

SQL&gt; insert into t1 select * from t1;

23849 rows created.

SQL&gt; insert into t1 select * from t1;

47698 rows created.

SQL&gt; insert into t1 select * from t1;

95396 rows created.

SQL&gt; insert into t1 select * from t1;

190792 rows created.

SQL&gt; insert into t1 select * from t1;

381584 rows created.

SQL&gt; commit;

Commit complete.

SQL&gt; conn bp/bp
Connected.
SQL&gt; select name, value from v$mystat mt join v$statname sn on (mt.statistic# = sn.statistic#) where sn.name in ('transaction rollbacks', 'rollback changes - undo records applied');

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
rollback changes - undo records applied                                   0
transaction rollbacks                                                     0

SQL&gt; set timing on
SQL&gt; update t1 set object_id = object_id + 1;
update t1 set object_id = object_id + 1
       *
ERROR at line 1:
ORA-01013: user requested cancel of current operation


Elapsed: 00:00:01.51

SQL&gt; select name, value from v$mystat mt join v$statname sn on (mt.statistic# = sn.statistic#) where sn.name in ('transaction rollbacks', 'rollback changes - undo records applied');

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
rollback changes - undo records applied                              173323
transaction rollbacks                                                     1

Elapsed: 00:00:00.00
SQL&gt;


1 transaction was rolled back and 173323 undo records were applied to perform the rollback. But that is because I had no other change in that transaction.

If I have other changes in the transaction, those changes will not be rolled back automatically:

SQL&gt; conn bp/bp
Connected.
SQL&gt; select name, value from v$mystat mt join v$statname sn on (mt.statistic# = sn.statistic#) where sn.name in ('transaction rollbacks', 'rollback changes - undo records applied');

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
rollback changes - undo records applied                                   0
transaction rollbacks                                                     0

Elapsed: 00:00:00.00
SQL&gt; insert into t1(object_id) values (-1);

1 row created.

Elapsed: 00:00:00.00
SQL&gt; select count(*) from t1 where object_id = -1;

  COUNT(*)
----------
         1

Elapsed: 00:00:00.09
SQL&gt; select name, value from v$mystat mt join v$statname sn on (mt.statistic# = sn.statistic#) where sn.name in ('transaction rollbacks', 'rollback changes - undo records applied');

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
rollback changes - undo records applied                                   0
transaction rollbacks                                                     0

Elapsed: 00:00:00.00
SQL&gt; update t1 set object_id = object_id + 1;
update t1 set object_id = object_id + 1
       *
ERROR at line 1:
ORA-01013: user requested cancel of current operation


Elapsed: 00:00:02.16

SQL&gt; select name, value from v$mystat mt join v$statname sn on (mt.statistic# = sn.statistic#) where sn.name in ('transaction rollbacks', 'rollback changes - undo records applied');

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
rollback changes - undo records applied                              274294
transaction rollbacks                                                     0

Elapsed: 00:00:00.01
SQL&gt; select count(*) from t1 where object_id = -1;

  COUNT(*)
----------
         1

Elapsed: 00:00:00.04
SQL&gt; rollback;

Rollback complete.

Elapsed: 00:00:00.00
SQL&gt; select count(*) from t1 where object_id = -1;

  COUNT(*)
----------
         0

Elapsed: 00:00:00.06
SQL&gt; select name, value from v$mystat mt join v$statname sn on (mt.statistic# = sn.statistic#) where sn.name in ('transaction rollbacks', 'rollback changes - undo records applied');

NAME                                                                  VALUE
---------------------------------------------------------------- ----------
rollback changes - undo records applied                              274295
transaction rollbacks                                                     1

Elapsed: 00:00:00.00


Notice how the value of transaction rollbacks remained 0 this time, and how the INSERT was not rolled back, and I was still able to rollback the transaction manually.