Oracle View上的更新速度极慢

Question

I have this simple UPDATE Statement:

  UPDATE   v_my_view mv
     SET   mv.name   = 
              (SELECT   RTRIM(name)
                 FROM   v_another_view av
                WHERE av.KEY_ID = mv.KEY_ID)
   WHERE mv.VALID = 1;

This Statement takes extremely long (20 secs), while other, more complicated updates on the same view take less than 1 second. First I thought it is the RTRIM function, but it's not, if I dont't use it, its slow as before.

SELECTs on both views return the records very fast.

There is no TRIGGER on the view, but there is one on the table behind. But it cannot be the bottleneck, since even when I comment all the TRIGGER code out, it has the same slow performance.

Anybody has a suggestion?

EDIT: Added missing WHERE clause EDIT: The view (or the table behind) contains only 8000 records each, no special data types.

Answer 1

You are updating the entire view without any WHERE clause.

If you have a big amount of data or even indexes, it could be slowing your operation.

Answer 2

Do you have any indexes on column name in underlying table of v_my_view ? If yes, disable them and see if it leads to any improvements on the performance of the query. As Nick.McDermaid puts it, it is hard to say without execution plans and wait event statistics. The best you can hope for is some form of psychic debugging.

Answer 3

merge --+ use_hash(MV,AV) no_merge(AV) no_merge(MV)
    into (select * from v_my_view MV where valid = 1)
using v_another_view AV
on MV.key_id = AV.key_id
when matched then
    update
    set MV.name = rtrim(AV.name)
;

Although I'm not absolutely sure about merge ing into an inline view, but you may try it at least (and post a comment if it does not work).

Also, it is a good practice to show execution plans of your queries along with the queries.