-- Перед каждым запуском делаю
RECREATE TABLE T (
    V  INTEGER
);

execute block as
declare variable I integer;
begin
  I = 1;
  while (I <= 10000000) do
  begin
    insert into T(V) values(:I);
    I = I + 1;
  end
end
-- Execute time = 43s 384ms
-- Execute time = 43s 509ms
-- Execute time = 43s 321ms

execute block as
declare variable I integer;
declare variable c integer;
begin
  c = 1;
  while (c <= 10) do
  begin
      in autonomous transaction do
      begin
          I = 1;
          while (I <= 1000000) do
          begin
            insert into T(V) values(:I);
            I = I + 1;
          end
      end
      c = c + 1;
  end
end
-- Execute time = 34s 211ms
-- Execute time = 35s 397ms
-- Execute time = 34s 960ms

/*
(43.384 + 43.509 + 43.321) / 3 = 43.4046666666667
(34.211 + 35.397 + 34.960) / 3 = 34.856
(43.4046666666667 - 34.856) / 43.4046666666667 * 100  = 19.6952708618122
*/