Select/Update taking far too long to run, how can I get it to go faster?

Question

Hello all,
I am trying to do an update/select on a table that returns 16 million records. So far most of the time it takes forever to complete or never finishes. Initially I was trying to do it as one big select, but when that didnt work, i broke it down to creating a table with the "base" 16 million records, and am trying to fetch additional values for each of those records from the table i grabbed those records from. Doing a select got me no where, so I am trying to do an update of the tables with the values i find using a cursor. Even this does not seem to be working. Is there a way to do it with a batch/bulk update that would be faster? The code is as follows: (oracle 10g):
DECLARE 
   CURSOR wr63993_cur IS
      SELECT   provider_id,
               din_gp_pin,
               orig_prescription_nbr,
               adjudication_date
        FROM   WR63993_BASE
       WHERE   adjudication_date BETWEEN to_date('2009/07/01', 'yyyy/mm/dd') AND to_date('2009/07/31', 'yyyy/mm/dd');
   CURSOR date_cur (v_provider_id WR63993_BASE.provider_id%TYPE,
                    v_din_gp_pin WR63993_BASE.din_gp_pin%TYPE,
                    v_orig_prescription_nbr WR63993_BASE.orig_prescription_nbr%TYPE,
                    v_adjudication_date WR63993_BASE.adjudication_date%TYPE)
      IS
      SELECT   MIN(adjudication_date) min_date
        FROM   claim_history@posi
       WHERE   provider_id = v_provider_id
         AND   din_gp_pin = v_din_gp_pin
         AND   orig_prescription_nbr = v_orig_prescription_nbr
         AND   adjudication_date >= ADD_MONTHS(v_adjudication_date, - 24);
BEGIN
   FOR wr63993_rec IN wr63993_cur LOOP
      FOR date_rec in date_cur(wr63993_rec.provider_id, wr63993_rec.din_gp_pin, wr63993_rec.orig_prescription_nbr, wr63993_rec.adjudication_date) LOOP
         UPDATE   WR63993_BASE
            SET   min_date = date_rec.min_date
          WHERE   provider_id = wr63993_rec.provider_id
            AND   din_gp_pin = wr63993_rec.din_gp_pin
            AND   orig_prescription_nbr = wr63993_rec.orig_prescription_nbr;
      END LOOP;
  END LOOP;
  COMMIT;
END;
/

Answer 1

aaah. healthcare insurance :)
The performance of these, as i'm sure you know, is tricky.
Consider the following which could help you eliminate your cursors. Here, B.adjudication_date will be the same as "MIN(adjudication_date) min_date" from your query.
I understand that this is typically outside of your control, but if it is at all possible, move all of the data to the same database so you don't need those distributed queries. Separate schemas is ok.
Select
  stuff
From Wr63993_Base A
Inner Join Claim_History@Posi B On A.Provider_Id=B.Provider_Id And A.Din_Gp_Pin=B.Din_Gp_Pin And A.Orig_Nbr=B.Orig_Nbr
--the next table will allow you to get *earlier* instances of the claim where the adjudication date was in past 24 months
--we only want to see the row where there ARE NO EARLIER instances. So this LOJ will return null for that row.
Left Outer Join Claim_History@Posi C On A.Provider_Id=C.Provider_Id And A.Din_Gp_Pin=C.Din_Gp_Pin And A.Orig_Nbr=C.Orig_Nbr
and c.adjudication_date >= ADD_MONTHS(a.adjudication_date, - 24) and c.adjudication_date<b.adjudication_date
Where  
  A.Adjudication_Date Between To_Date('2009/07/01', 'yyyy/mm/dd')
  And To_Date('2009/07/31', 'yyyy/mm/dd')
  And B.Adjudication_Date >= Add_Months(A.Adjudication_Date, - 24)
  and c.adjudication_date is null --only get the row where B is the earliest qualifying adjudication date.
Dave