Question

假设我有一个包含两列TABLE和COL_1的表COL_2。

我有一个只显示TABLE.COL_1的物化视图，其设置为：REFRESH FAST ON COMMIT。

如果我更新TABLE.COL_2，物化视图是否会刷新？

Answer 1

是的，似乎更新COL_2还会刷新视图。

更新COL_2比没有物化视图的类似表上的类似更新使用更多资源。更新COL_2将更新实例化视图的行时间戳（ORA_ROWSCN）。

-------
--Compare the amount of work done to update.
--The difference isn't huge, but is significant and consistent.
-------

--Create table and materialized view
create table table1 (col_1 number primary key, col_2 number);
create materialized view log on table1;
create materialized view table1_mv refresh fast on commit
  as select col_1 from table1;
insert into table1 values(1, 1);
commit;

--Create a regular table for comparison
create table table2 (col_1 number primary key, col_2 number);
insert into table2 values(1, 1);
commit;

--Parse the queries so traces won't count that work.
update table1 set col_1 = 2;
update table1 set col_2 = 2;
update table2 set col_1 = 2;
update table2 set col_2 = 2;
rollback;

set autotrace on
alter system flush buffer_cache;
update table1 set col_1 = 2;
--         11  db block gets
--          8  consistent gets
--         13  physical reads

rollback;
alter system flush buffer_cache;
update table1 set col_2 = 2;
--          6  db block gets
--          8  consistent gets
--         12  physical reads

rollback;
alter system flush buffer_cache;    
update table2 set col_1 = 2;
--          7  db block gets
--          7  consistent gets
--          9  physical reads

rollback;
alter system flush buffer_cache;
update table2 set col_2 = 2;
--          3  db block gets
--          7  consistent gets
--          8  physical reads

set autotrace off


-------
--Compare ORA_ROWSCN.
--The times are different, implying the materialized view was modified.
-------

--(You may need to run these steps slowly to reproduce.  ORA_ROWSCN is
--not perfect, sometimes you'll see the same timestamp.)
select scn_to_timestamp(ora_rowscn) from table1_mv;
    --3/5/2011 12:25:25.000000000 AM
update table1 set col_1 = 3;
commit;
select scn_to_timestamp(ora_rowscn) from table1_mv;
    --3/5/2011 12:25:37.000000000 AM
update table1 set col_2 = 3;
commit;
select scn_to_timestamp(ora_rowscn) from table1_mv;
    --3/5/2011 12:25:46.000000000 AM

物化视图刷新提交

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