* A simple deadlock example

-- From session 1 at time t1
SQL> update test3 set c2=7 where c1='y';

1 row updated.

-- From session 2 at time t2
SQL> update test3 set c2=5 where c1='b';

1 row updated.

-- From session 1 at time t3
SQL> update test3 set c2=8 where c1='b';  <-- process hangs at time t3, waiting for session 2 to complete
update test3 set c2=8 where c1='b'        <-- ORA-00060 at time t5
       *
ERROR at line 1:
ORA-00060: deadlock detected while waiting for resource

-- From session 2 at time t4
SQL> update test3 set c2=9 where c1='y';  <-- process hangs at time t4, waiting for session 1 to complete

1 row updated.                            <-- process resumed at time t7

SQL> 

-- From session 1 at time t6 
SQL> rollback;

Rollback complete.

SQL>