Session 1                                  commit
|-------------------------------------------->

{1,2,3} ∈ P                         {1,2,3,4} ∈ P

              Session 2: single update statement
              |------------------------------------------------------>

              {1,2,3} ∈ P                   4 ignored              updated for {1,2,3}

Session 1                                  commit
|-------------------------------------------->

{1,2,3} ∈ P                                  {1,2} ∈ P

              Session 2: single update statement
              |------------------------------/ restart

              {1,2,3} ∈ P
                                             /----------------------->

                                             {1,2} ∈ P             updated for {1,2}

create table test(
id int,
flag int,
val int
);

insert into test values (1, 1, 0);
insert into test values (2, 1, 0);
insert into test values (3, 1, 0);
insert into test values (4, 0, 0);
insert into test values (5, 0, 0);
commit;

select * from test;

        ID       FLAG        VAL
---------- ---------- ----------

         1          1          0
         2          1          0
         3          1          0
         4          0          0
         5          0          0

Session 1

update test set flag = 1 where id = 4; -- добавлям новую строку id=4 удовлетворяющую предикату

update test set val = 100 where id = 1;

select * from test;

        ID       FLAG        VAL
---------- ---------- ----------

         1          1        100
         2          1          0
         3          1          0
         4          1          0
         5          0          0

Session 2

update test set val = 100 where flag = 1;
-- ожидание


Session 1

commit;

Session 2

-- продолжение после ожидания

3 rows updated.

select * from test;

        ID       FLAG        VAL
---------- ---------- ----------

         1          1        100
         2          1        100
         3          1        100
         4          1          0 -- новая строка с id=4 проигнорирована

         5          0          0

select * from test;

        ID       FLAG        VAL
---------- ---------- ----------

         1          1          0
         2          1          0
         3          1          0
         4          0          0
         5          0          0

Session 1

update test set flag = 0 where id = 3; -- строка id=3 больше не удовлетворяет предикату

update test set val = 100 where id = 1;

select * from test;

        ID       FLAG        VAL
---------- ---------- ----------

         1          1        100
         2          1          0
         3          0          0
         4          0          0
         5          0          0

Session 2

update test set val = 100 where flag = 1;
-- ожидание


Session 1

commit;

Session 2

-- продолжение после ожидания

2 rows updated.

select * from test;

        ID       FLAG        VAL
---------- ---------- ----------

         1          1        100
         2          1        100
         3          0          0 -- Oracle учел что строка с id=3 уже не удовлетворяет предикату 

                                 -- и выполнил update для нового набора строк

         4          0          0
         5          0          0

create or replace package logpkg is
cnt int;
end;
/

create or replace function gen100 return number
is
begin
logpkg.cnt := logpkg.cnt + 1;
return 100;
end;
/

SQL> exec logpkg.cnt := 0;

PL/SQL procedure successfully completed.

SQL> update test set val = gen100() where flag = 1;

3 rows updated.

        ID       FLAG        VAL
---------- ---------- ----------

         1          1        100
         2          1        100
         3          1        100
         4          1          0
         5          0          0

SQL> exec dbms_output.put_line(logpkg.cnt);
3

PL/SQL procedure successfully completed.

SQL> exec logpkg.cnt := 0;

PL/SQL procedure successfully completed.

SQL> update test set val = gen100() where flag = 1;

2 rows updated.

SQL> select * from test;

        ID       FLAG        VAL
---------- ---------- ----------

         1          1        100
         2          1        100
         3          0          0
         4          0          0
         5          0          0

SQL> exec dbms_output.put_line(logpkg.cnt);
5

PL/SQL procedure successfully completed.