Performance issue with inline view in Oracle

Question

I have a query that looks like below and the tables A,T,S have around 1 million rows whereas P have more than 100 million rows. I've newly introduced the inline view "temp" into this query and it caused a drastic degradation in performance. The data retrieved for temp is hardly 50 rows and this inline query runs in a snap when executed alone.

The autotrace statistics show a huge increase in the number of "consistent gets" from a 6 digit number before introducing temp to a 9 digit number after adding this!! Also, more than 90% of LAST_CR_BUFFER_GETS are accounted for the "temp" view. If I extract the data from this view into a temporary table and use that table as part of the joins the performance is very good but that solution is not really feasible for me.

I know the question is very generalized but I'm wondering if there is anything trivially wrong in using this inline view. Doesn't inline views give the same performance like having this data in a temporary table? Is there any way I can hint Oracle to use this view in a effective manner and thus increasing performance.

   select t.id, 
          a.date
     from A a,
          T t,
          P p,
          S s,
          (select id 
             from S, 
                  R 
            where s.id = r.id 
              and r.code  = 10
                  r.code1 = 20
                  r.name  = 'string1' ) temp
    where ...cond1
          ...cond2
          ...cond2
    s.id = temp.id

Answer 1

Best guess, based on my tuning experience is it's probably evaluating the inline view "temp" once per records matched from the result-set obtained by joining A, t, p, s. The best solution here is to re-write it this way. Keep in mind that the ORDERED hint assumes that you are providing the tables in the FROM clause in the order in which you want them to join. I've listed temp and s first, cos that's the only join condition you have listed temp.id = s.id. Also I'm assuming you have indexes on all the other columns that are part of the join criteria. Let me know if you have any more questions.

select  /*+ ordered use_nl(a t p s) */
    t.id,  a.date
from    (
    select  id 
    from    S, 
        R
    where   s.id = r.id and r.code  = 10 r.code1 = 20 r.name  = 'string1' 
    ) temp,
    S s,
    A a,
    T t,
    P p
where   ...cond1 ...cond2 ...cond2 and s.id = temp.id