select 1 from "SCOTT"."MLOG$_TABLE2" where rownum=1

drop materialized view mv_table1;
drop table table1 purge;
drop table table2 purge;

create table table1(
  a integer primary key,
  b date,
  c varchar2(16)
);

create table table2(
  a integer primary key,
  b date,
  c varchar2(16)
);

create materialized view log on table1
with rowid, sequence, commit scn ( b, c ) including new values;

create materialized view log on table2
with rowid, sequence, commit scn ( b, c ) including new values;

create materialized view mv_table1 (b, c, cnt)
refresh fast on demand
as 
select b, c, count(*) cnt
from   table1 
group by b, c;

SQL> set timing on
SQL> exec dbms_mview.refresh('MV_TABLE1','F');
 
PL/SQL procedure successfully completed
 
Executed in 0,25 seconds

insert into table2(a,b,c)
with get_data(a,b,c,i) as (
  select 1 a,trunc(sysdate) b,to_char(sysdate,'yyyy-mm-dd')||'-'||1 c, 2 i from dual
  union all
  select i, trunc(sysdate)+mod(i,10000),to_char(sysdate+mod(i,10000),'yyyy-mm-dd')||'-'||mod(i,10000), i + 1
  from   get_data
  where  i<= 3000000
)
select a,b,c
from   get_data;

SQL> set timing on
SQL> exec dbms_mview.refresh('MV_TABLE1','F');
 
PL/SQL procedure successfully completed
 
Executed in 5,367 seconds

select 1 from "SCOTT"."MLOG$_TABLE2" where rownum=1

SQL> exec dbms_mview.refresh('MV_TABLE1','F');

SQL ID: 89s2c53j480vz Plan Hash: 1479141652

select 1
from
 "SCOTT"."MLOG$_TABLE2" where rownum=1


call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          4          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        1      5.88       5.89          0    3058867          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        3      5.88       5.89          0    3058871          0           0

Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: SYS   (recursive depth: 1)
Number of plan statistics captured: 1

Rows (1st) Rows (avg) Rows (max)  Row Source Operation
---------- ---------- ----------  ---------------------------------------------------
         0          0          0  COUNT STOPKEY (cr=3058867 pr=0 pw=0 time=5891187 us)
         0          0          0   TABLE ACCESS FULL MLOG$_TABLE2 (cr=3058867 pr=0 pw=0 time=5891181 us cost=7990 size=0 card=1)