create table t ( x primary key, y not null ) as
  select rownum x, rownum y from dual connect by level <= 1000;

create materialized view log on t;  
create materialized view mv 
  partition by range (x) (
    partition p0 values less than (501),
    partition p1 values less than (1001),
    partition pmax values less than (maxvalue)
  ) 
  refresh fast on demand as 
  select * from t;
  
insert into t values (0, 0);
commit;

select x from mlog$_t;

         X
----------
         0

select count(*) from mv partition (p1) ;

  COUNT(*)
----------
       500

alter table mv merge partitions p0, p1 
  into partition p1 update global indexes;

select count(*) from mv partition (p1) ;

  COUNT(*)
----------
      1000

alter table mv split partition p1 at (100) 
  into (partition p0, partition p1) update global indexes;

select count(*) from mv partition (p1) ;

  COUNT(*)
----------
       901

select x from mlog$_t;

         X
----------
         0

exec dbms_mview.refresh('mv', 'F');

select * from mv where x = 0;

         X          Y
---------- ----------
         0          0