Data Warehouse Cursor Problem

Question

I am trying to complete a piece of work for College but am having trouble with the completion of a cursor. The object of this small project is to create a very basic data warehouse from an operational system.
I have populated all of the dimension tables except one which is to be populated with the FACT table. These tables are to be populated with the cursor I am trying to complete.
I having difficulty understanding what the first select statement in the cursor does. For the region dimension table, I was asked to create a sequence to use as the primary key (region_id). The region_id in the operational table has different values e.g. 6000, 6001.
'dw_op' is the schema on the operation table which is accessed through the DB link 'q_link'.
Any thoughts on what is required to complete this cursor would be a big help.
Here is the incomplete anonymous block and cursor:
declare
     cursor c_sales is
          select order_line.product_id, order_line.quantity,
          product.unit_cost, product.unit_price, ord.client_id,
          ord.SALES_REP_ID, ord.order_date from dw_op.ord@q_link, dw_op.order_line@q_link,
          dw_op.product@q_link
          where ord.order_id = order_line.order_id AND
          order_line.product_id = product.product_id...
     s_value number;
     s_cost number;
     begin
     for c_rec in c_sales loop
          select region_id into r_id
          from region where region_name =
               (select region_name from dw_op.sales_region@q_link,
               dw_op.sales_rep@q_link where sales_region.region_id =
               sales_rep.region_id and SR_id = c_rec.SALES_REP_ID);
          select time_seq.nextval into s_time from dual;
          Insert into time values (s_time, s_day, s_month, s_year ... );
          s_value := ... // how much it costs the company, unit_price * something?
          s_cost := ... // time something by the quantity
INSERT INTO sale VALUES (ord.client_id, order_line.product_id, ord.SALES_REP_ID, r_id, s_time, order_line.quantity,
s_value, s_cost); // need to find out how to enter select info into table
     end loop
end;

Answer 1

You may have an IO problem but you may also have a design issue/configuration issue. what you are seeing is multiple session waiting for the same block, if 20 sessions all request the same block one will read it form disk (db file scattered read or db file sequential read) and 19 session will wailt on read by other session and then get the block from the cache.
there do seem to be a very high number of waits for read by other session in the database so you may want to investigate exactly what sql is waiting on this event and if you could benifit form either a larger buffer cache or using te keep and recycle pools to manage frequently accessed tables better. Otherwise investigate the SQL that is perfomring the most IO and tune it to do less work.
Chris